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Community and Regional Planning Program
University of Texas School of Architecture
Austin, Texas
Rainwater Harvesting Systems for Residential and Commercial
Systems:
Seaholm Power Plant and Radiance Community
Urban Environmental Analysis
CRP 383: Fall 2005
Community and Regional Planning ProgramUniversity of Texas School of Architecture
Austin, Texas
July, 2006
Analysis Prepared and Presented By:
Professor:Kent Butler
Ahmed Abukhater
Jason Fryer
Ashley FrancisKyle Irons
Andrew JuddWonsoo Lee
Nathan MeadeVipin Nambiar
Mary-Elaine Sotos
July, 2006
Additional Research:
Acknowledgements
We would like to thank the following:
Seaholm Power Plant Development:
John Rosato
Southwest Strategies Group
Radiance Community Development:
Roger Kew
Radiance Water Supply Corp.
Proofreading:
Christa Arnold
Urban Environmental Analysis
CRP 383: Fall 2005
Community and Regional Planning ProgramUniversity of Texas School of Architecture
Austin, Texas
July, 2006
Table of Contents
Integrated Water Resource Management Integrated Water Resource Management 01 Rainwater Harvesting 05 Storm Water Management 10
Seaholm Power Plant Seaholm Power Plant 13 Water Demand Modeling 16 Economic Analysis 21 Recommendations 25
Radiance Community Radiance Community 27 Water Demand Modeling 31 Economic Analysis 36 Recommendations 43
Appendices 44 sedoC ytefaS :A xidneppA 15 sedoC htlaeH :B xidneppA 35 etiS mlohaeS :C xidneppA 55 ataD detaleR retaW saxeT :D xidneppA 85 ledoM dnameD mlohaeS :E xidneppA
Appendix F: Stormwater Considerations at Seaholm 67 96 soiranecS ecnaidaR :G xidneppA 47 gniledoM ecnaidaR :H xidneppA
Appendix I: Radiance Economic Analysis 80Appendix J: Notes on Cost Analysis and Cisterns 85 Appendix K: Cost Analysis and Monthly Savings 87
09 sisylanA tsoC mlohaeS :L xidneppA
Integrated Water Resource Management
Background:
Integrated Water Resource Management (IWRM) has become a popular concept in
the practice of sustainable design and of resource management, and its sudden prominence
has led many to believe that IWRM is a new concept, created specifically to address current
water shortages. However, the true origins of IWRM can actually be found hundreds,
perhaps even thousands, of years ago. Evidence exists that both the Romans and the
Egyptians may have practiced Integrated Water Resource Management well before the birth
of Christ, but even discounting the contributions of these two remarkable civilizations,
tangible evidence is still available dating as far back as the tenth century. In Valencia, Spain,
the government was already forming participatory water tribunals to address the four major
components of Integrated Water Resource Management (Rahaman & Varis, 2005). While
the Spanish, in 1926, were perhaps the first officially to adapt IRWM as an organizational
model for water management (Embid, 2003), water resource management was adapted still in
the United States by the Tennessee Valley Authority as early as the 1940’s (Tortajada 2004).
In more recent years, Integrated Resource Water Management has been applied or has been
recommended in many cases and numerous examples of these programs began to develop
globally in the 1970’s and ‘80’s. However, despite its newfound prevalence, Integrated
Resource Water Management did not intrude upon the public awareness until the last ten
years as water management and water cost issues have become increasingly pressing and the
call for Integrated Resource Water Management was finally added to the agenda of several
world wide environmental conferences.
Definition:
In 2002, the Technical Advisory Committee of the Global Water Partnership offered
to Johannesburg World Summit the following definition of Integrated Water Resource
Management:
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[Integrated Water Resource Management is] a process, which promotes the coordinated development and management of water, land and related resources in order to maximize the resultant economic and social welfare in an equitable manner without compromising the sustainability of vital systems. Rahaman & Varis, 2005
This definition was used to set forth the basic goals of Integrated Resource Water
Management, and at the Johannesburg World Conference it was further suggested that these
principles should be applied within the bailiwick of good government and public
participation (Johannesburg, 2002). Unfortunately, despite all of the progress made by the
conference attendees, the final definition for Integrated Resource Water Management
manages to omit any concrete instructions for the technical aspects of IRWM, proffering
lofty ideals without providing any practical insight into the application of or the development
of an integrated water system.
Technical Aspects:
Integrated Water Resource Management has been hailed as a panacea for all the
world’s water problems; it is effective not only against short-term water shortages and cost
increases but also against the impending water crises of the future. After the Johannesburg
World Conference ended, both public and private individuals struggled with the application
of definition provided by the Technical Advisory Committee into a practical model for water
conservation and usage. In their report on Integrated Water Management for the Central
Texas Hill Country, Kent Butler and Andrew Karnoven suggest using an integrated approach
for water management (2004). Broken down to its basic components, Butler and Karnoven’s
integrated approach consists of the following four concerns that have been further refined by
the Urban Analysis Seminar at the University of Texas:
1. Water Demand: By analyzing water demand data in an integrated management
system it becomes possible to influence the water system systemically. The water
system infrastructure can be customized to fit the actual usage, thus reducing wasted
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resources, and, in turn, this demand data can be used to educate the consumer and
hopefully to promote water conservation. The interplay of these two variables,
system size and actual water consumption, can be eventually mediated to produce a
more efficient allocation of water resources.
2. Water Supply: Hand in hand with the emphasis on water demand comes a focus on
the water supply itself. As water demand can only be reduced to a certain level, it
becomes necessary to balance conservation efforts with an increase in the volume of
water available to meet these demands. Rainwater collection, desalination
procedures, or wind harvesting each offer viable alternatives to a traditional well or to
a municipal water system.
3. Water Reuse and Reclamation: The third aspect of this integrated approach lies in
the reclamation of water from wastewater and from sewage. By focusing on water
reclamation and on rehabilitation, additional sources of water are created and these
procedures further ease the burden placed on the current water supply.
4. Storm Water Management: The final piece of the integrated water systems puzzle
is critical concern in modern building situations involving the treatment and the
disposition of storm water runoff. Besides being an additional source of usable water,
storm water management is also important to prevent surface erosion and to maintain
a healthy environment capable of contributing to an Integrated Water Resource
Management System.
Justifications:
The ultimate goal of any Integrated Water resource Management is the effective and
the efficient use of an important and of an increasingly scarce natural resource: water. To
accomplish this all four issues referenced above must be considered as well as the following
questions suggested by Butler and Karnoven:
1. How much water is actually used onsite by the new development? 2. What are the options for water supply sources, and what are the
tradeoffs?
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3. How much sanitary wastewater and storm water runoff is generated on the site, and what are their likely water quality impacts under different control strategies?
4. Can the various water uses and supplies in a new development be better integrated so as to create more efficient, less consumptive water services?
5. What is the economic feasibility of each of the multiple scenarios and their respective water services?
6. More specifically, how feasible are some of the newer practices, such as rainwater harvesting, in terms of technical requirements and user acceptance on a subdivision scale, or an urban development?
Butler & Karnoven, 2004
The ultimate goal for devising an Integrated Resource Water Management program is to
reduce the impact from a given site on the water supply both upstream and downstream. By
carefully considering all six of the above questions, as well as the four components of the
water system listed previously, it should become possible to achieve at least some modicum
of success.
4
Rainwater Harvesting Systems
Background
Much like Integrated Water Resource Management, rainwater harvesting not only has
begun to enjoy a newfound popularity, but also is a relatively antiquated concept.
Archeologists have found physical evidence of rainwater storage cisterns in Israel dating as
far back as 2000 B.C., with written evidence suggesting that the concept of rainwater
collection and storage techniques existed in China circa 4000 B.C. (Texas Water
Development Board, 2005). In early
twentieth century Texas, rainwater
collection systems received extensive
usage until municipal water supplies
became financially feasible and
readily available, causing rainwater
systems to wane both in popularity
and in frequency (Krishna, 2003).
However, in the last several decades,
rainwater systems have resurged with
increasing frequency, particularly in
the more arid regions of the southwestern United States, where water shortages are rampant
and municipal water costs are on the rise. Currently in the United States, approximately
100,000 residential rainwater systems have been implemented, including more than 400
professionally installed, full-scale water harvesting systems in Central Texas alone. This
number is constantly on the rise, especially in cities such as Austin, Texas, where the city has
espoused a commitment toward sustainability and toward green building, going so far as to
offer incentive programs that have been responsible for the creation of over 6,000 rainwater
barrels in the city alone (Water Development Board, 2005).
Figure 1. Chinese Cisterns for Rainwater Storage
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Components
Rainwater harvesting is based on a very simple concept: collecting falling rain and
storing it for later use. To that end, a rainwater system can be as simple as a barrel set out in
storm to collect water for
a small garden, or it can
be complex enough to
satisfy the water supply
for an entire building.
Despite the vast
differences in complexity
and design, most domestic
rainwater systems are
made up of six main
components (Water
Development Board,
2005):
1. Catchment system: Many common rainwater systems will use the building’s
existing rooftop as a surface to collect the rainwater, although many newer systems
will add a pole barn or rain barn as a structure that provides additional surface area to
maximize the volume of water harvested.
2. Gutters and downspouts: Most houses already have existing gutters; however, it is
often advisable to upgrade these existing gutters when adding a rainwater system.
When installing gutters for a rainwater system, care is essential to correctly size the
gutters to handle the flow of water from the roof, and if the system is designated for
potable water, the gutters should be inspected for lead seams that can contaminate the
water supply.
3. Leaf guards: Leaf guards take several different shapes from funnels to baskets and
can be made of a myriad of materials, from nylon to stainless steel. Regardless of the
specific form, every leaf guard has a similar function: keeping the system clean and
Figure 2. Residential Rainwater System
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maintaining the flow of water from the catchment surface to the storage area. In
addition to a leaf guard, many systems also include a first-flush diverter. This system
allows the first fraction of a rainfall to wash the rooftop and helps to remove any
debris and any detritus present on the roof.
4. Storage tanks: Often referred to as cisterns, the storage tank is one of the central
aspects of any rainwater system. All the water collected from the rooftop is first
stored in the storage tanks before it is re-implemented for use. As storage tanks get
more expensive when their volume increases, the tank size is often the determining
and the limiting factor in the capacity of a rainwater system (Appendix J).
5. Delivery system: Once the water is collected in the storage tank, a system is needed
to transport the water from the tank to the tap or into the house. While a gravity fed
system would be ideal, it is often necessary to add a pressure tank or a pump to
increase the water pressure into the house. Water only gains approximately one psi of
pressure for every 2.3 feet of vertical drop and most municipal water systems supply
between 40 psi and 60 psi to their domestic users; most internal water systems are not
designed to operate below this level. Even typical irrigation systems will require
between 15 psi to 20 psi to function properly.
6. Filtration system: A filtration system is suggested for all rainwater systems, but it
should be mandatory if the system is deigned for potable water. Various systems can
be installed, utilizing mechanical, chemical or even ultraviolet systems, and a
professional should be consulted before installing any rainwater system that is
intended for potable use.
General Concerns:
In spite of the relative simplicity of implanting a rainwater system, several serious
concerns must still be addressed. Both the Texas Commission for Environmental Quality
and the Texas Department of Health supply guidelines and regulations concerning the use
and treatment of water garnered from a rainwater harvesting system. The largest issue
central to both of these sets of code involves the end use of the water supply: potable (fit for
human consumption) or non-potable (not fit for human consumption).
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• Potable Water: Potable water sources are generally dealt with under TCEQ Title 30
Part 1 Chapter 290 Subchapter D (Appendix A). This code sets forth guidelines and
requirements for the treatment of potable water sources. The TCEQ also put forth
requirements for the physical design of the system, the most important of which is the
need to maintain a separation between municipal water systems and rainwater
systems. The need to prevent cross-contamination can be satisfied by the insertion of
an air gap between the two systems or the use of a back flow prevention system.
• Non-Potable Water: Non-Potable water supplies have fewer requirements on their
implementation, but general guidelines are supplied by the Texas Department of
Health and can be found in Sections 341.037, 341.038 and 341.039 of the Texas
Administrative Code. The majority of the issues involved deal with public safety and
the elimination of public nuisances, but these codes should be consulted when
installing any type of rainwater harvesting system (Appendix B).
The TCEQ also provides a list of guidelines for water safety and for quality, as well as a
definition of public versus private water systems. Many of these issues are only suggestions
until the water system reaches a certain size, but the specific guidelines can be found either
by contacting the TCEQ or by checking their comprehensive website.
Benefits:
The obvious benefit derived from the use of a rainwater system is of course the
availability of a low cost alternative to the municipal water supply. However, the cost issue
only begins to scratch the surface when exploring reasons for the use of a rainwater system.
Due to rainwater’s nearly neutral pH and its general lack of impurities it is superior to ground
water or even to municipal water supplies for a host of reasons (Krishna, 2003):
1. Taste and Purity: Users of potable rainwater systems enjoy a higher purity of water
and, consequently, a better tasting supply.
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2. Soft Water: Rainwater is naturally a soft water and the lack of minerals eliminates
the need for a water softener. Additionally, the mineral deficit causes less wear on
appliances and on fixtures, lowering maintenance costs.
3. Contaminant Free: In addition to being naturally sodium free, thereby satisfying an
increasingly important dietary requirement, rainwater is free of many of the chemicals
that are added to municipal water supplies.
4. Natural Quality: Stored rainwater has been shown to be especially effective for
irrigation purposes; plants tend to thrive more from this source than from municipal
or from treated water.
Despite the obvious advantages, rainwater systems are not always viewed as economically
feasible. However, in addition to the purity issues qualified above, rainwater systems also
allow users to reduce the burden on the water supply during peak demand as well as
providing an alternative means to manage storm water runoff. The argument against
rainwater systems is that it is not fiscally viable when municipal water sources are present
(Peterson, 2005), but this counterpoint is only true in the narrowest view of the benefits of
rainwater systems. Balancing the palpable costs of installing a rainwater system against all
of the intangible benefits it provides is a difficult task; it becomes problematic to place a
strict monetary value on the importance of purity and of taste, or on the ability to reduce the
ravages of storm water runoff. However, this difficulty should not be allowed to discourage
the implementation of rainwater systems and in the future the advantages gained from their
use should far outweigh the systems’ monetary value.
9
Storm Water Management
Background
Under the traditional practice of storm water management, rainwater flows from yards
out into the street and into storm sewers. Impervious surfaces such as rooftops, driveways,
plazas, and streets do not allow rainwater to infiltrate into the soil. Consequently, water
flows quickly and in great volumes to streams and to lakes. Storm water carries sediments
and pollutants such as chemicals and fertilizers to creeks and rivers, causing the
contamination of potential drinking water and impacting the food chain that supports the
indigenous fish population. By keeping as much rainwater as possible in to proximity to
where it falls and by collecting and reusing this water, we can reduce adverse impacts on our
lakes and streams.
In the past, the primary concern centered on the removal of storm water runoff as quickly
as possible from the developed areas to achieve a convenient and a protected environment.
Channeling runoff with storm sewers, swales, gutters, and channels to the nearest water body
was, historically, the first line of defense. A more recent philosophy of storm water
management is to address on-site runoff by developing a comprehensive, integrated
approach, which contends with not only water quality but also to volume and to the rate of
runoff. Consequently, hydrologic problems can be minimized by preserving and by
maintaining the predevelopment drainage patterns to the greatest extent possible.
Further Studies Needed
It is necessary to explore the technical aspects of storm water for both of the projects in
greater detail. This includes understanding of the existing hydrologic characteristics as well
as engineering for the proposed system, which will establish size, storage capacity, discharge,
and infiltration rates. Further studies are needed to discern the amount of water generated
from the site and therefore the corresponding size of the storage tanks required to
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accommodate the excess water runoff. Technical studies must be conducted to evaluate the
adequacy and the capacity of the infrastructure in both projects.
11
Seaholm Power Plant:
Study on the Feasibility of Installing a Rainwater
Harvesting System for Irrigation
Community and Regional Planning Program
University of Texas School of Architecture
Austin, Texas
December, 2005
Seaholm Power Plant
Built between 1950 and 1958, the Seaholm Power plant sits adjacent to Austin’s
Town Lake. During its lifetime, it housed five gas turbines and was capable of producing
approximately 100 megawatts of power. By the 1980s, the plant had ceased to produce
energy and was saved only in 1984 when a Historic Resources survey designated the
Seaholm Plant as a high priority historic building. Shortly thereafter, the City of Austin’s
Town Lake Comprehensive Plan “suggested that the plant be ‘converted into an activity
center complimentary to the area’ (City of Austin, 2000).” Thirteen years later the
Regional/Urban Design Assistance Team agreed with this recommendation and the
Seaholm Power Plant Reuse program was born.
The Seaholm Power Plant is located on West Cesar Chavez, in Austin, Texas.
The power plant sits on an eight-acre site on the north side of Town Lake, facing the
water. The site has been reconditioned
and following extensive clean up
operations, has been certified as safe for
human inhabitation and as
environmentally sound (Novak, 2006).
The five large gas turbines have been
removed from the interior of the
building, but much of the original
structure is still in place. The remaining
building consists of two subterranean
floors and a main floor with sixty-five
foot ceilings. The overall structure
measures approximately 110 feet by 235
feet and encompasses more than 100,000
square feet (Backus, 2005). Despite the
industrial nature of the structure, light
streams through two flanking rows of
Figure 1. Aerial View: Seaholm Power Plant
13
clerestory lights near the ceiling to create an open, inviting, and naturally illuminated
space with potentially vibrant reuse.
Renovation Plans:
In April 2005, after the environmental cleanup and recovery of the Seaholm site
and approval of the EPA, the City of Austin selected the Seaholm Power, LLC
consortium to facilitate the renovations at the Seaholm Power Plant. Their mission
statement: to “build a dynamic urban center around Seaholm’s Power Plant as part of a
financially responsible public/ private partnership” (Landis, 2005). To this end, Seaholm,
LLC has suggested an environment open 24/7 to the public domain that will house Austin
City Limits and the new KLRU studio. The interior of the power plant will also host
commercial, retail and unprogrammed public spaces, while the exterior of the building
will feature a new multi-story office building and a ten-story residential tower (Appendix
C). In addition to these new residents, the site will also reflect the City of Austin’s
commitment to green building and to sustainability, represented primarily by a rainwater
collection and harvesting system that will optimize the extensive roof area covering the
existing buildings. Specific details of the proposed facility can be found in the Executive
Summary for the Seaholm Master Plan on the City of Austin’s website:
http://coapublish1.ci.austin.tx.us/.
Rainwater Supply
The rainfall data in the models is based on the median rainfall of the Austin, TX
region over the past seventy-five years. The median rainfall derived from this data was
24.17 inches per year. It is assumed that only 90% (ninety) of the total rainwater is
caught by the rainwater system. The rooftops evaluated in the models consist of the
existing Seaholm Powerplant (approximately 35,000 square feet), and the proposed office
building (approximately 30,500 square feet). It must be noted, however, that certain
schemes use these rooftops differently.
14
Rainwater Collection:
With approximately 65,000 square feet of rooftop surface available for collection
of rainwater, a rainwater system could be devised that would provide non-potable water
for use on site. This system would provide several different benefits not only for the
Seaholm Project, but also for the City of Austin itself. The rainwater collected from the
roof could be stored and then used to satisfy the irrigation requirements for the entire
development. Additionally, depending on the design of the rainwater harvesting system,
excess water could also be diverted to fountains and to other architectural elements, thus
severely reducing the load on the city municipal water system while also promoting
responsible water use throughout the remainder of the city. A secondary benefit derived
from the use of a rainwater system is the ability to control storm water runoff. The large
roof areas combined with extensive swaths of impervious ground cover create a site that
is extremely susceptible to the ravages of storm water runoff, and the site’s proximity to
Town Lake further increase the need to address critical storm water concerns (Appendix
F).
15
Water Demand Modeling
The purpose of modeling the water demands for a commercial rainwater
collection system was the analysis of various different combinations of rooftop collection
areas, rainwater storage needs, and water demands to find the optimal amount of
rainwater to be harvested to supplement the need for municipal water. The Seaholm
Power Plant development incorporates a mixture of uses, landscaping, and paving on the
existing site, Figure 2. The model intends to analyze the benefits of a hybrid system that
Figure 2. Seaholm Plant Proposed Development
16
meets its demands through different ratios of rainwater and of municipal water. In
addition to supplementing municipal water, the rainwater system also decreases the load
imposed on the municipal storm water system by capturing much of the rainwater that
would otherwise be directed into the surrounding storm water system. Most of the
scenarios evaluated are mixed systems; that is, those that use a combination of rainwater
and of municipal water to meet their demands for water. The models have been further
segregated into intended implementations of the collected rainwater as well as the ratios
of rainwater used versus municipal water used. Each of the scenarios was developed in
conjunction with an economic analysis to find the required system components and
eventually the cost of parts and the maintenance that would result from each.
A rainwater collection coefficient of 0.9 gallons of water per square foot of roof
area for every inch of rainfall was used for calculating the total rainwater that could be
collected. The coefficient ensures that the model incorporates concerns regarding losses
occurring from phenomena such as roof surface evaporation and associated with roof
washing, among others. The rainfall data used in the model is the regional median rainfall
rate beginning in 1930 and calculated monthly over a seventy-five year period (Appendix
D). The comprehensive nature of the data ensures that the model incorporates climatic
uncertainties that are typically tied to the effective functioning of a rain water system.
Each of the model’s scenarios was established with the intent of developing a hybrid
system to meet as much of the total demand as possible with rainwater without acquiring
large surplus or a deficit of water storage at the end of the year. Thus, the tanks were
sized in such a way that minimal water was spilled, and the ratio of demands met by
rainwater was determined by the comparison of the amount of rainwater collected and the
water demands of each month. Although the “end-of-month storage” fluctuated heavily
due to higher irrigation needs and lower rainwater collection amounts in the hot, arid
months, the system’s storage level at the end of the year was approximately even with
minimal net gain or loss.
The rooftops evaluated in the models consist of the existing Seaholm Power Plant
(approximately 35,000 square feet), and the proposed office building (approximately
17
30,500 square feet), Figure 3. Each scenario uses the optimal combination of rooftop
collection areas needed to accrue the desired
amount of rainfall necessary to meet the typical
demand as determined by earlier analysis.
There is existing water storage, approximately
57,000 gallons, located in the power plant just
south of the Seaholm Power Plant, Figure 4.
The models revealed that this storage would
need to be supplemented, regardless of the
collected water’s expected use, therefore requiring additional rainwater storage tanks.
Each scenario requires differing quantities of additional storage ranging from 30,000
gallons to 100,000 gallons in order to produce an optimal system. The water demand
analyzed in the models is derived from multiple factors.
First, the outdoor water demands consist primarily of the irrigation of more than
65,000 square feet of landscaping, and filling decorative fountains that are approximately
12,800 square feet, Figure 4. It was assumed that the landscaping area consisted of three
major water categories of water demand: low, medium, and high water use. It was
assumed that 70% (seventy) of the
landscaping would be medium water use,
20% (twenty) would be high water use, and
10% (ten) would be low water use. Each of
these categories relates to the amount of
irrigation required in comparison to the
amount of water that is evaporated as a
result of climatic factors. The demand for
Figure 3. Rainwater Collection Areas
Figure 4. Rainwater Storage Locations
18
the fountains was based on a similar evaporation factor known as “pan evaporation rate”
(Appendix D). An additional evapotranspiration factor of 1.2 was used to account for the
additional loss of water as a result of spraying fountains, since the developers described
them as “decorative.” The greater surface area and the result of the wind on the spraying
water increases the amount of water lost above that of the pan evaporation rate. It also
was assumed that the fountain was filled with 25,000 gallons of municipal water prior to
running the system.
Second, the indoor water demands required consideration. In this development, it
was assumed that rainwater would only be used for non-potable (non-drinking) purposes,
such as the flushing of toilets in the Seaholm Power Plant building and in the proposed
office building. These values derived from a projected number of visitors and of
employees per day in each of the facilities. Using the International Building Code, the
quantities of occupants per square foot were
found based on the values given for the
usable square footages of the pertinent
buildings of the proposed development.
After finding the expected number of
occupants per day in addition to the typical
water demands of office employees and
retail visitors in the Austin area, the total
water demand for each month was
calculated.
Analysis
The intent of this model is the exploration of the possibility of a rainwater
harvesting system to be incorporated into the proposed Seaholm Power Plant
redevelopment. It was an interest of the developer to explore the rainwater harvesting
system both for economic and for environmental reasons. The models aim to calculate
the amount of water demand that can be met with various combinations of rainwater
Figure 5. Proposed Landscaping
19
harvesting systems when applied to the proposed designs of the site. Therefore, to
examine the varying scales of rainwater collection systems possible for the Seaholm
Project, the model includes four design scenarios. While details of each scenario and
their subsequent evaluations can be found in Appendix E, the four scenarios can be
summarized by the following:
• Scenario A – Irrigation with 30,000 gallons added storage
• Scenario B – Irrigation with office bldg and 60,000 gallons added storage
• Scenario C – Irrigation and fountains with 100,000 gallons added storage
• Scenario D – Irrigation, fountains, toilets w/100,000 gallons added storage
Results
Each of the scenarios has unique advantages and disadvantages, but two in
particular appear most efficient. Scenarios B and C were able to implement effectively
the most amount of water in terms of what was collected. Although they both had
increased rainwater catchment areas from the proposed office building, they were also
able to use almost the entirety of what was collected due to the lower demands and
increased storage than in Scenario D. Scenario A showed that the Seaholm Power Plant
rooftop alone is insufficient to meet all of the landscape irrigation needs, but was able
still to fulfill over 50% (fifty) of them. The existing storage also was inadequate, since
the large roof area spilled a large volume of water during the months of heavy rainfall.
Scenario D appeared to be the most inefficient, because the addition of the indoor water
demands for toilet flushing was too great for the amount of rooftop collection per month.
It resulted in large deficits of rainwater use as well as resulting in a usage rate of only
36% (thirty-six), the lowest of the four scenarios.
20
Economic Analysis
The economic analysis model for the Seaholm project will compare the costs
associated with the four rainwater collection system scenarios to the cost of water
supplied by the city of Austin. Water price forecasting has indicated probable increases
in municipal water prices so the economic analysis model will include water price
inflation at 0% (zero), 1% (one), 2% (two), and 3% (three) percent, respectively, over
inflation itself, which is assumed to be 2% (two). Costs for the majority of the rainwater
collection system components in the Seaholm Project were obtained from the RS Means
2005 Building Construction Cost Data guidebook. It should be noted, though, that
because the Seaholm Project is a large-scale and complex development project, the costs
obtained for the economic analysis are very approximate and could be more or less,
depending upon project site issues and upon the final construction plans.
Similar to residential projects, the majority of the cost of a commercial rainwater
collection system is storage facilities (Appendix J). Additional storage volume clearly
can provide a greater volume of water available for use. Additional water supplied by the
system exponentially increases the benefit of the rainwater system. However, from an
economic perspective, storage should only be increased to a volume which can be
reliably filled and consumed by the collection and utilization system, otherwise the
potential benefit created through the cost of additional storage cannot be obtained.
For the Seaholm project, because of the high aesthetic priority, tanks placed above
ground are not an option. All of the scenarios include additional storage facilities and
only subterranean tanks will be considered in the analysis. Piping is required to connect
and to distribute water among the various collection, storage, and usage components.
Other required elements are pumping and filtration equipment. There are a large variety
of pumps that have the potential to be used in various design scenarios. The pumping
configuration will depend on specific storage elevation and site data and on irrigation
equipment pressure requirements. As a consideration towards implementation, system
maintenance costs were included in addition to the equipment replacement costs.
21
Although it is assumed building maintenance will have the capability to perform the
majority of maintenance tasks, an additional $50 monthly charge was included in the
system costs to account for minor system repairs, for adjustments, and for testing.
In the economic analysis, the cost of the rainwater system is measured the cost
avoided (through the collection of rainwater) of the volume of water which would have
been supplied by the water utility. Water is supplied to Seaholm from the Austin Water
Utility and the current 2005 rates are available on the City of Austin website:
www.ci.austin.tx.us/water/rateswr05.htm. For commercial customers such as Seaholm
water rates are $3.38 per 1000 gallons during the off peak season (November 1 through
June 30) and $3.62 per 1000 gallons during the peak season (July 1 through October 31).
For the purposes of this analysis, $3.50 per 1000 gallons will be used as the water cost
avoided through rainwater collection.
Creating the Financial Model for Economic Analysis
To analyze the economic aspects of the Seaholm rainwater collections system, a
financial model was created. The model was designed to allow the user the flexibility to
update inputs and to study the system costs as well as water savings implications over a
fifty-year time period. All replacement and maintenance costs are adjusted for inflation,
assuming an increase of 2% (two) annually. Water utility pricing was studied by
increasing increments of inflation above the model’s 2% (two) rate by 1% (one)
increments. The financial model considers four design scenarios and compares the
construction, the maintenance, and the replacement costs of those four options with the
cost savings generated from the water volume harvested (Appendix L).
Results
The accuracy of the economic analysis relies on the quality of the input data. For
the purposes of this study, the inputs have been fixed, based on information obtained
through research and through communication with various project representatives.
22
However, the value of the financial model is in the flexibility to refine inputs based on
more current research and on a more current understanding of the projects needs and of
its planned direction.
The Seaholm economic analysis looks at the relation of the estimated total future water
cost savings to the estimated total installation and maintenance costs of the rainwater
collection system on a yearly basis for each of the four design scenarios. The economic
model indicates that all rainwater system design scenarios under every water price
inflation factor have payback periods within the fifty-year analysis period. This result
suggests that from an economic perspective, almost any scale of rainwater harvesting
system at Seaholm will be a viable project. Table 1 summarizes the payback periods for
the four design scenarios.
As Figure 6 demonstrates, Scenario B has the shortest payback period, with a
scaled-down version of the system, represented by Scenario A, having slightly longer
payback periods. Scenarios C and D, which expand the rainwater collection to supply
other water uses like exterior
fountains and like indoor
toilets, have longer payback
periods due to the gratuitous
costs associated with the
additional storage and
conveyance equipment
required to configure the
rainwater system to serve those
purposes. This result suggests that financially, it is more beneficial to align the rainwater
collection system to serve as few purposes as completely as possible, than to partially
supply a larger, more diverse number of uses for the water. The payback periods for
Scenarios A and B also illustrate that as long as the water price inflation rate is a
minimum of one 1% (one) above normal inflation (represented by 3% (three) inflation),
the return on investment for the Seaholm rainwater harvesting system will take
Figure 6. Payback Periods
Years to Achieve Return on Investment Water Price Inflation (%)
Scenario 2 3 4 5 A 29 23 20 19 B 27 21 20 18 C 34 29 26 22 D 46 36 30 27
23
approximately twenty years to achieve. The minimal one to two year decreases in
payback period shown with each 1% (one) increase in water price inflation rates indicate
that Scenarios A and B are less sensitive to water price inflation and that the return on
investment will most likely be achieved within a maximum thirty-year time frame under
any water pricing scenario that does not involve a decrease in the price of water. For the
Seaholm project, Scenario B would yield the greatest economic benefit by providing the
most rapid return on investment and because of the larger volume of water it supplies,
offering the greatest savings per year for the cost of the system above the savings which
could be attained under Scenario A.
24
Recommendations
Management Recommendations
The Texas Manual for Rainwater Harvesting recommends that county health
department staff and city building code staff be consulted concerning the construction of
the rainwater harvesting system and subsequent safe, sanitary operations. It is assumed
that the rainwater system installer will contact the necessary parties. To maintain safe
and sanitary operations, we recommend that the system and the landscape that it supports
be maintained by a dedicated landscape management company. It is not necessary that
they be on site full-time, however. Additionally, it is imperative that the company hired
be familiar with rainwater collection system, and it would be beneficial to have their
involvement from the inception so that they have a thorough understanding of the
components, the conveyance systems, and their integration in the landscape.
Monitoring Recommendations
The water collected at Seaholm will be non-potable but, because the water will
inevitably come into contact with humans, we recommend that the levels of certain
pathogens in the water be monitored regularly [The Texas Manual for Rainwater
Harvesting 2002]. Routine maintenance operations should be conducted to confirm that
the system is performing properly and efficiently. Additionally, disinfection systems
such as the automated chlorination system must undergo routine testing to ensure the
highest level of functionality.
25
Radiance Community:
Study on the Feasibility of Installing a Rainwater
Harvesting System as an Alternative Water Supply
Community and Regional Planning Program
University of Texas School of Architecture
Austin, Texas
December, 2005
Radiance Community
Located approximately thirty minutes west of downtown Austin, the Radiance
Community sits within a housing development in the Texas Hill Country. The
community itself is comprised of approximately forty lots and the developers and the
inhabitants share a common desire to tread lightly on their environment. With this goal
in mind, the Radiance Community contacted the University of Texas in hopes of
determining the feasibility of harvesting rainwater in an attempt to eliminate the need for
municipal water services.
Integrated Water Resource Management
To facilitate the process of completing a feasibility study for the Radiance
Community, the board members provided a
complete documentation of the water
demand for their community, as well as
detailed information on the water usage
patterns of the individual homes. This data
revealed that the Radiance Community’s
desire to adopt a rainwater harvesting
system was only a small piece of a larger
Integrated Water Resource Management
Plan. Analyzing the demand and the usage
data from the community, it is clear that many of the households within Radiance are
already involved in conservation efforts and in the regulation of water demand, the first
component of an IWRM. The desire for a rainwater system, coupled with the use of
community wells, clearly embodies the second tenet of an integrated system, while their
exploration of wastewater processing and of reclamation supports the third requirement
of water reclamation and reuse. The final piece of an integrated water program, storm
water management, while not specifically discussed, is nevertheless modulated by the use
Figure 1. Typical Radiance Household
27
of any rainwater harvesting system, creating a complete picture of Integrated Water
Resource Management.
Radiance Residential Development
With respect to the site design of the project, the main challenge is achieving
integration of specific management devices into the existing landscape. Many design
issues must be taken into account, some of which are safety, cost, maintenance, site
suitability, and appropriateness and multiple use. To reduce the risk of erosion, protection
is necessary at the outlet of all pips and paved channels where the flow velocity exceeds
the permissible velocity of the receiving channel or area. Structurally lined aprons or
other energy-dissipating devices are commonly used.
In addition, Best Management Practices (BMPs) can be adopted to reduce pollution,
to control runoff, and to integrate with the natural and the built landscape. Management
practices that include wet ponds, detention facilities, infiltration facilities, and waste
quality basins can be used singly or in a combinative effort. Devisers are channels that
direct excess water away from areas where it is unwanted and diverts it to areas where it
can be disposed appropriately. Reducing the impervious surface areas, especially parking
lots, can also reduce storm water runoff
quantities as well as minimizing
construction and maintenance costs. As
shown in Figure 2, the use of permeable
paving is a recommended alternative for
low-traffic parking areas, for emergency
access roads, and for driveways. The use of
natural landscape provides important
benefits for water quality and for the habitat
itself in addition to its lower costs for
installation and for maintenance than those
of conventional landscaping. Figure 2. Permeable Pavement
28
Radiance Project
A municipal water utility collects, treats, and distributes water to various facilities
with the equipment, the operation, and the maintenance costs incorporated into the fee
that the utility company charges the water users for their volume of water utilized. With
residential rainwater collection, the various components of the water supply system are
located on the property of the residence and they are owned, operated, and maintained by
the person who lives there. In the economic analysis we will be disregarding non-
monetary motivations for installing rainwater collection such as water resource
conservation and as environmental stewardship and focus solely on a cost comparison of
rainwater collection water supply systems and the foregone cost of drilling a new well.
The Radiance Water Supply
Corporation distributes water to
the majority of the thirty-six
residences in the Radiance
subdivision with a couple of
homes within the community
already using rainwater
collection as their water supply.
The water source utilized by the
Radiance Water Supply
Corporation is Edward’s Aquifer
that is pumped from a well
located on the Radiance property.
Cost considerations for this water
supply include the lifespan of the
well and of distribution facilities;
however, creating an accurate Figure 3. Residential Rainwater Harvesting System
29
economic model for the municipal water supply is outside the scope of this analysis and
instead, the cost comparison will be based on the current price per gallon for well water.
A rainwater collection system is essentially made up of three main subsystems: a
capture subsystem, a storage subsystem, and a distribution subsystem (Figure 3). The
capture subsystem includes the roof, the gutters, and the roof washer/diverter; the storage
subsystem consists of the storage tank, and the distribution system includes a pump and
filtration and treatment equipment if the water is to be used for potable purposes. Piping,
typically PVC, is used to connect the three subsystems. A few of the system components,
such as the roof, the gutters, and the interior piping, are features of a residence that are
present whether there is a rainwater collection system or not, and therefore will not be
included in the economic analysis. Installation and maintenance costs, with the exception
of part replacement, are not included in the economic analysis either, because they are
negligible in comparison to the costs associated with buying the equipment itself
necessary for rainwater collection. Because the Radiance project involves converting
houses from a well water to a rainwater system there could be additional costs and
difficulties associated with installing the rainwater system such as excavation, grading,
and plumbing modifications which are difficult to quantify on a broad basis, but should
be considered are on a site-specific basis, and subsequently added to the economic
analysis.
30
Water Demand Modeling
Water Demand
An important consideration in determining the successful transition from municipal or
from well water to a rainwater system lies within the water usage patterns of the
Radiance Community. With their strict adherence to their goal of minimizing the impact
on the environment, many households have already adopted water conservation habits.
The water demand data for the current Radiance inhabitants reveals that many households
are already using less water than comparably sized households in other communities.
The data is further reinforced by a physical inspection of the Radiance Community.
Many of the households already maintain and utilize high-efficiency fixtures and
appliances inside their homes, and the irrigation demands of their landscaping has been
reduced by specifically choosing indigenous plants suited to the climate that require less
irrigation (Appendix D).
The Radiance subdivision has a varied pattern of water consumption among its
members’ houses; thus the design of a rainwater collection system here must account for
the disparate levels of water demand while ascertaining the feasibility of such a system
within the current consumption pattern of each house. Since it is impractical to run water-
demand models for each house individually, a series of models have been developed
addressing various combinations of water consumption patterns for indoor and outdoor
water use. These models establish the volume of rainwater that could be captured
effectively and stored throughout the year to aid in the reduction of the total water supply
required from the Radiance Water Supply Corporation. The models, as seen in Appendix
G, have been developed with three categories of consumption; low, average, and high,
each developed using water consumption data accumulated within the subdivision over
the last five years. Presumably most houses would fit within the definition of average-
usage scenario, unless an extreme consumption pattern has been recorded. The low and
high scenarios, respectively, have been developed to account for these extreme users. The
31
models have been further segregated into intended categories of use for the collected
rainwater. The ideal scenario uses rainwater to service the combined outdoor and indoor
water demand, but models have also been developed to study the ability of a rainwater
system to meet specific indoor or outdoor demands.
The models also help estimate the appropriate cistern dimensions necessary for an
independent rainwater system. Based on an aggregated monthly water
demand/consumption pattern acquired from the Radiance Water Supply Corporation, a
rainwater collection coefficient of 0.623 gallons of water per square foot roof area for
every inch of rainfall was used for calculating the total rainwater that could be collected.
A collection efficiency rate of 90% (ninety) was used to ensure that the model
incorporates concerns about losses occurring from phenomena such as roof surface
Figure 4. Consumption Scenarios
32
evaporation and with roof washing, among others. The rainfall data used in the model is
the monthly median rainfall rate in the region calculated, beginning in 1930, over a
seventy-five year period. The comprehensive nature of the data ensures that the model
incorporates climatic uncertainties that are typically linked to the effective functioning of
a rainwater system (Appendix D). The model also assumes that the average roof size in
the subdivision is around 1600 sq. ft.; a few optimized models were further tested for
effectiveness with larger roof sizes; these have been discussed Appendix G.
In order to simplify and to visually interpret the results of each model/scenario to be
discussed later, Figures 4 and 5 are presented. Figure 4 displays all scenario combinations
(low, average, and high consumption vs. indoor only, outdoor only, and combined indoor
and outdoor usage) adjacent to each other for ease of comparison. Each cell displays a
percentage in the upper left-hand corner, which indicates the percentage of demand that
can be met with rainwater alone. In the lower right-hand corner, a circle with one of three
color gradations is displayed to facilitate a quick reference of the practicality of a given
scenario combination. The practicality of a scenario is based on a few inter-related
factors and as a result of the factors overlapping; some residents may or may not
necessarily agree with the practicality designated. Factors considered are as follows:
1. Demand Satisfied vs. Tank Size/Cost :
• How much demand would be met, and would the return be significant enough
to render the tank required to contain that amount of water cost effective?
2. Excess Generated vs. Tank Size/Cost Increase:
• Will the amount of water collected be excessive to the point of unacceptable
spillage?
• Will the tank size require significant increase only to contain surplus rainfall
accumulated, not necessarily to amass the amount of water needed to meet the
demand for water?
3. Ultimate Practicality:
33
• Does a combination of factors 1 and 2 make the scenario seem particularly
unappealing?
• Does it simply satisfy so little demand that it is unwise to endure the necessary
process of installation and its comparably associated cost?
With the above stated factors considered, the gradations seen in Figures 4 and 5 indicate
an infeasible/very unpractical scenario, a moderately feasible/practical scenario, or a very
feasible/highly practical scenario. The practicality of a scenario, as seen below the tables
in Figures 4 and 5, increase as the color changes from red to green (left to right – very
unpractical to highly practical).
Results
Figure 5. Consumption Scenario Results
34
The analysis performed under the above mentioned consumption scenarios
concludes that it might be significantly advantageous for users under the average
consumption scenario to use a rainwater system for combined indoor/outdoor and for
indoor water use. Specific details of this analysis can be found in Appendix G. It is
additionally beneficial for houses with larger roof areas to install these systems as they
can meet up to half of their water needs through these rainwater systems. Under the low
consumption scenario almost all of the water requirement, both indoor and outdoor, can
be met using rainwater. An approximate roof size of 1850 square feet would meet 100%
water demand for these houses. The high-consumption scenario has a significantly higher
water demand from the previous scenarios. Given the cost of installation of these
systems, high-consumption houses using rainwater for indoor use was found to be most
feasible as with a large enough roof size, almost 34% (thirty-four) of indoor water use
could be met with this system.
.
35
Radiance Economic Report
Rainwater collection is a completely self-contained form of water supply. Unlike
municipal water utility supply where the cost of water is based on the volume supplied by
the utility company, rainwater collection the water is free and the cost is contained in the
price of the collection system equipment, and the installation of and the maintenance of
the system itself. An economic analysis of a rainwater collection system is based on the
price of the various systemic components and the replacement costs of the individual
parts, which, in turn are dependent on the volume of water to be collected and stored and
its determined function (Appendix J).
This section analyzes the economic feasibility of a residential system for the Radiance
community in Hays County. This project involves a fairly typical residential conversion
from well water supply to individual rainwater collection for the Radiance houses, with
the potential implementation throughout the entire community to be managed by the
existing Radiance Water Supply Corporation. Costs for the residential rainwater
collection systems are well established and can be obtained from several websites listed
in this report.
This economic assessment looks at two different scenario groups. The first scenario
group will analyze the cost of implementing a rainwater collection system in one
household and compare this cost with the reduction in water bill from the Radiance Water
Supply Corporation. The second scenario will analyze the cost of implementing
rainwater collection systems on a much larger scale in the Radiance community.
The Financial Model
A financial model was created to study the economic implications of rainwater
collection for the Radiance project. The model was designed to allow the user the
36
flexibility to update inputs and study the implications over a fifty-year time period. All
costs are inflation-adjusted assuming a rate of 2% (two) annually.
The Radiance project analysis studies the retrofit and the installation of rainwater
collection systems within a residential community for assorted levels of consumption and
of uses. This examination determines the financial feasibility of rainwater collection
through the comparison of rainwater system lifestyle costs to the combined current water
expenditures and the supplemental savings accrued by not replacing a well. The model
allows the input of the following variables: the cost of all components of rainwater
collection system, the interval of part replacement, a factor for installation and for
transportation costs as well as the average water bill under a household’s current supply.
See Figure 6 for a sample input box for low-consumption household.
Figure 6. Sample Results for Low-Consumption Household
Low Consumption Square Feet 1600 Ave. monthly savings $ 9.05
Installation Factor 15%
Item Cost/Unit Total
Replacement Intervals (years)
Replacement Cost
Roof washer $ 850.00 $ 850.00 50 N/A
Tank (10,000g) $ 4,290.00 $ 4,290.00 50 N/A
Pump $ 585.00 $ 585.00 8 $ 585.00
Filter assembly $ 325.00 $ 325.00 50 N/A
3 & 5 micron filter* $ 100.00 $ 100.00 1 $ 100.00
UV light $ 675.00 $ 675.00 1.2 $ 80.00
Piping $ 3.00 $ 150.00 50 N/A
Electricity $ 0.07 $ 25.55 N/A N/A
* 1 year is a pack (12) 5 micrion filters and (4) 3 micron filters
37
Economic Analysis
The accuracy of the economic analysis relies on the quality of the input data. For the
purposes of this study, the inputs have been fixed based on information obtained through
research and through communication with specific project representatives. However, the
inherent value of the fiscal summation is in its flexibility to refine inputs based on clearer
current research and on a greater contemporary conception of projects’ needs and of their
planned direction. As previously mentioned, this analysis does not include any non-
monetary factors that may make rainwater harvesting increasingly attractive.
Implementation of Individual Rainwater Harvesting System
Rainwater collection systems for consumers with various needs including
irrigation (outdoor only) and potable (both indoor and outdoor) using costs to purchase,
to install, and to maintain the systems have been studied. The costs of systems will also
be analyzed for users with low, medium and high water demand and will be compared to
the cost savings from a reduced water utility bill.
Outdoor Indoor/Outdoor
Low Consumption $ 7,044 $ 7,936
Medium Consumption $ 7,528 $ 8,419
High Consumption $ 8,580 $ 9,471
There is a model in Appendix K that calculates the monthly water bill for a Radiance
customer based on the current rate structure. The cost of single rainwater collection
systems is shown in Figure 7.
Costs from this table represent the fixed, up-front cost of purchasing and of installing
a rainwater collection system. They include the tank itself, the filter assembly, the filters,
the UV lighting, the pumps, the roof washers and the piping. A tank size differs based on
Figure 7. Implementation Costs
38
the consumption rates. A 6,000-gallon tank was deemed appropriate for the low-
consumption users, an 8,000 gallon for medium-consumption users and an 11,000 one for
high-consumption users. These costs do not reflect the long-term maintenance costs such
as the replacing of filters and of pumps and the cost of electricity. These expenditures
will be included later in this report. The price of the outdoor systems does not include
filtration systems. The filtration of the indoor systems consists of a series of filters, 5-
micron and 3-micron, a UV light for disinfection and a filter board. A 15% (fifteen)
disbursement increase was added to these systems to defray installation and
transportation. This percentage is a variable and can be modified in the model for a
customer who wants to self-perform any or all of this work. Fiberglass has been selected
as the optimal tank material due to its long-term durability, its thermal properties and its
reasonable price, but alternatives do exist (Appendix J). A summary of all the expenses
provided in the tables above can be found in Appendix K.
In a single-home scenario, the cost of the rainwater systems can be compared to the
savings accrued on the water bill and on associated well water from using the Radiance
services. It should be duly noted that this expenditure differential would only be realized
if a very limited number of households implement a rainwater collection system because
the majority of the operational expenses of the water supply corporation are fixed.
Therefore, to generate the current amount of revenue (that which is required to support
the Radiance Water Supply Corporation) the corporation will be forced to raise rates on
the existing water usage to pay for its own fixed costs. This increase will theoretically
nullify any savings from a rainwater collection system on a community-wide application.
The community-wide application is discussed in a supplementary scenario.
39
Long-term expenses such as replacement costs and as electricity play a major role in
the economic feasibility of a rainwater collection system. A 2% (two) inflation factor
was also added. Figure 8 shows the fifty-year costs and savings for a medium-
consumption user with both indoor and outdoor uses. This figure shows that the
monetary outflow outweighs the savings over a fifty-year lifecycle of the system. The
two lines actually diverge, demonstrating that the recurring maintenance costs are higher
than the continued payment to the Radiance water supply corporation.
In total, nine figures were evaluated, varying the consumption from low, from
medium, and from high and varying the uses as indoor, outdoor and indoor and outdoor.
The indoor and outdoor scenario was also studied in conjunction with a larger roof
catchment surface. These nine figures can be found in the Appendix I. In only one
scenario did the savings from the rainwater collection system outweigh the expense of the
system: Low-Consumption with a large roof. This scenario is represented in Figure 9,
and demonstrates that the cost of the rainwater collection systems exceeded the savings
reaped in approximately the thirty-sixth year of operation, largely because the large roof
area provides sufficient catchment area for the low-consumption user to sustain average
water demands without supplement from the Radiance water supply corporation. This
Cost Analysis: Medium Consumption, Indoor & Outdoor
$-
$5,000.00
$10,000.00
$15,000.00
$20,000.00
$25,000.00
$30,000.00
$35,000.00
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
Time (Yrs.)
Cum
ulat
ive
Cos
t ($)
Costs
Savings
Figure 8. Cost Anaylsis
40
independence will allow the user to forego the $22 monthly water service fee as well as
the municipal water fees.
Implementation of Community-Wide Rainwater Harvesting System
Like most well water users, the Radiance community is faced with the imminent
necessity for a new well, as the existing loses its ability for adequate production to
support community. The cost of drilling a new well is loosely comparable to that of
installing rainwater collection systems in the Radiance community, an effort that will
lessen the strain on the existing well. However, the authors of this paper cannot forecast
precisely the level of decreased demand necessary to prolong the life of the existing well.
Figure 10 shows the cost of implementing rainwater collection systems for half of and for
all of the households, respectively, in the Radiance community, and the corresponding
gallons of rainwater used.
The cost of implementing rainwater collection systems over half of the homes in
Radiance slightly exceeds $136,000. This number assumes a 10% (ten) discount from
bulk purchasing savings, and from delivery and from installation savings. The
implementation expense of rainwater collection systems in all of the radiance homes is
Cost Analysis: Low Consumption, Indoor & Outdoor, Large Roof
$-
$5,000.00
$10,000.00
$15,000.00
$20,000.00
$25,000.00
$30,000.00
$35,000.00
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
Time (Yrs.)
Cum
ulat
ive
Cos
t ($)
Costs
Savings
Figure 9. Cost Analysis
41
roughly $258,000, which includes a discount factor of 15% (fifteen). All figures were
extrapolated from the average cost of a medium-consumption household for indoor and
outdoor use.
A potential economic benefit of implementing rainwater collection systems over a
large portion of the community is the savings from not replacing the current well as the
strain on existing well is drastically diminished. The depth of drilling [to reach a water
source] will determine the expense of drilling a new well, but the likely sum centers
around $40,000. It appears that the amount of money required in attaining this $40,000
savings is much larger than the actual savings itself, deigning this scenario unfeasible
from an economic standpoint. As previously mentioned, the amount of water savings to
make the existing well sustainable is not known. Additional analysis should be
performed to further understand this issue. The table above estimates gallons of
rainwater used based on the medium consumption household for indoor and outdoor use
so that a future comparison can be made.
As many users in the surrounding areas continue to pump water at a very high rate,
the viability of well water is declining and ultimately may cease. In this scenario, the
cost of implementing rainwater collection systems to the Radiance community should be
compared to the foregone cost of other water sources.
Cost of Systems Rainwater Used per Year (gal)
Half of Radiance $ 136,392 389,232
All of Radiance $ 257,630 778,464
Figure 10. Implementation Costs
42
Recommendations
Management Recommendations
To assist the homeowners, we recommend that the Radiance Water Supply
Corporation contact a rainwater system installer to consult. This consultant would
provide general design, management, routine maintenance guidelines and assistance for
all homes and would be on call if issues subsequently should arise. As each rainwater
system will be run independently, each individual homeowner will manage their own
collection system, and should monitor tank levels, maintain unobstructed gutters and
first-flush devices, change out filters regularly, maintain disinfection equipment and test
not only the water quality and but also the system functions regularly.
Monitoring Recommendations
The Texas Manual for Rainwater Harvesting recommends that both county health
department and city building code staff be consulted concerning the construction of the
rainwater collection system and the subsequent safe, sanitary operations. It is assumed
that the rainwater system installer will contact the necessary parties. Because the water
collected here will be potable, in accordance with the recommendations from the Texas
Manual for Rainwater Harvesting, we recommend that the harvested rainwater be tested
quarterly for fecal coliforms, pathogens, and pesticides by a commercial analytical
laboratory [Texas Manual for Rainwater Harvesting 2002]. Additionally, although
neither federal nor state guidelines exist for harvested water quality, one should check the
Environmental Protection Agency’s website [www.epa.gov/safewater/mcl.html] for a list
of the latest drinking water requirements before ordering specific tests. Most
commercial laboratories [consult your local Yellow Pages: Laboratories—Analytical and
Testing for a list of local testing laboratories] will test for pathogens, metals and
pesticides and the Texas Department of State Health Services
[www.dshs.state.tx.us/lab/default.shtm] will test for fecal coliforms.
43
Appendix A: Safety Codes Excerpt from Texas Administrative Code: Title 30, part 1, Chapter 290, Subchapter D, Rule § 290.39: (a) Authority for requirements. Texas Health and Safety Code (THSC), Chapter 341, Subchapter C prescribes the duties of the commission relating to the regulation and control of public drinking water systems in the state. The statute requires that the commission ensure that public water systems: supply safe drinking water in adequate quantities, are financially stable and technically sound, promote use of regional and area-wide drinking water systems, and review completed plans and specifications and business plans for all contemplated public water systems not exempted by THSC, §341.035(d). The statute also requires the commission be notified of any subsequent material changes, improvements, additions, or alterations in existing systems and, consider compliance history in approving new or modified public water systems. (b) Reason for this subchapter and minimum criteria. This subchapter has been adopted to ensure regionalization and area-wide options are fully considered, the inclusion of all data essential for comprehensive consideration of the contemplated project, or improvements, additions, alterations, or changes thereto and to establish minimum standardized public health design criteria in compliance with existing state statutes and in accordance with good public health engineering practices. In addition, minimum acceptable financial, managerial, technical, and operating practices must be specified to ensure that facilities are properly operated to produce and distribute a safe, potable water. (c) Required actions and approvals prior to construction. A person may not begin construction of a public drinking water supply system unless the executive director determines the following requirements have been satisfied and approves construction of the proposed system. (1) A person proposing to install a public drinking water system within the extraterritorial jurisdiction of a municipality; or within 1/2-mile of the corporate boundaries of a district, or other political subdivision providing the same service; or within 1/2-mile of a certificated service area boundary of any other water service provider shall provide to the executive director evidence that: (A) written application for service was made to that provider; and (B) all application requirements of the service provider were satisfied, including the payment of related fees. (2) A person may submit a request for an exception to the requirements of paragraph (1) of this subsection if the application fees will create a hardship on the person. The request must be accompanied by evidence documenting the financial hardship. (3) A person who is not required to complete the steps in paragraph (1) of this subsection, or who completes the steps in paragraph (1) of this subsection and is denied service or determines that the existing provider's cost estimate is not feasible for the development to be served, shall submit to the executive director: (A) plans and specifications for the system; and (B) a business plan for the system.
44
(d) Submission of plans. (1) Plans, specifications, and related documents will not be considered unless they have been prepared under the direction of a licensed professional engineer. All engineering documents must have engineering seals, signatures, and dates affixed in accordance with the rules of the Texas Board of Professional Engineers. (2) Detailed plans must be submitted for examination at least 30 days prior to the time that approval, comments or recommendations are desired. From this, it is not to be inferred that final action will be forthcoming within the time mentioned. (3) The limits of approval are as follows. (A) The commission's public drinking water program furnishes consultation services as a reviewing body only, and its licensed professional engineers may neither act as design engineers nor furnish detailed estimates. (B) The commission's public drinking water program does not examine plans and specifications in regard to the structural features of design, such as strength of concrete or adequacy of reinforcing. Only the features covered by this subchapter will be reviewed. (C) The consulting engineer and/or owner must provide surveillance adequate to assure that facilities will be constructed according to approved plans and must notify the executive director in writing upon completion of all work. Planning materials shall be submitted to the Texas Commission on Environmental Quality, Water Supply Division, MC 153, P.O. Box 13087, Austin, Texas 78711-3087. (e) Submission of planning material. In general, the planning material submitted shall conform to the following requirements. (1) Engineering reports are required for new water systems and all surface water treatment plants. Engineering reports are also required when design or capacity deficiencies are identified in an existing system. The engineering report shall include, at least, coverage of the following items: (A) statement of the problem or problems; (B) present and future areas to be served, with population data; (C) the source, with quantity and quality of water available; (D) present and estimated future maximum and minimum water quantity demands; (E) description of proposed site and surroundings for the water works facilities; (F) type of treatment, equipment, and capacity of facilities; (G) basic design data, including pumping capacities, water storage and flexibility of system operation under normal and emergency conditions; and (H) the adequacy of the facilities with regard to delivery capacity and pressure throughout the system. (2) All plans and drawings submitted may be printed on any of the various papers which give distinct lines. All prints must be clear, legible and assembled to facilitate review. (A) The relative location of all facilities which are pertinent to the specific project shall be shown. (B) The location of all abandoned or inactive wells within 1/4-mile of a proposed well site shall be shown or reported. (C) If staged construction is anticipated, the overall plan shall be presented, even though a portion of the construction may be deferred. (D) A general map or plan of the municipality, water district, or area to be served shall accompany each proposal for a new water supply system.
45
(3) Specifications for construction of facilities shall accompany all plans. If a process or equipment which may be subject to probationary acceptance because of limited application or use in Texas is proposed, the executive director may give limited approval. In such a case, the owner must be given a bonded guarantee from the manufacturer covering acceptable performance. The specifications shall include a statement that such a bonded guarantee will be provided to the owner and shall also specify those conditions under which the bond will be forfeited. Such a bond will be transferrable. The bond shall be retained by the owner and transferred when a change in ownership occurs. (4) A copy of each fully executed sanitary control easement and any other documentation demonstrating compliance with §290.41(c)(1)(F) of this title (relating to Water Sources) shall be provided to the executive director prior to placing the well into service. Each original easement document, if obtained, must be recorded in the deed records at the county courthouse. Section 290.47(c) of this title (relating to Appendices) includes a suggested form. (5) Construction features and siting of all facilities for new water systems and for major improvements to existing water systems must be in conformity with applicable commission rules. (f) Submission of business plans. The prospective owner of the system or the person responsible for managing and operating the system must submit a business plan to the executive director that demonstrates that the owner or operator of the system has available the financial, managerial, and technical capability to ensure future operation of the system in accordance with applicable laws and rules. The executive director may order the prospective owner or operator to demonstrate financial assurance to operate the system in accordance with applicable laws and rules as specified in Chapter 37, Subchapter O of this title (relating to Financial Assurance for Public Drinking Water Systems and Utilities), or as specified by commission rule, unless the executive director finds that the business plan demonstrates adequate financial capability. A business plan shall include the information and be presented in a format prescribed by the executive director. For community water systems, the business plan shall contain, at a minimum, the following elements: (1) description of areas and population to be served by the potential system; (2) description of drinking water supply systems within a two-mile radius of the proposed system, copies of written requests seeking to obtain service from each of those drinking water supply systems, and copies of the responses to the written requests; (3) time line for construction of the system and commencement of operations; (4) identification of and costs of alternative sources of supply; (5) selection of the alternative to be used and the basis for that selection; (6) identification of the person or entity which owns or will own the drinking water system and any identifiable future owners of the drinking water system; (7) identification of any other businesses and public drinking water system(s) owned or operated by the applicant, owner(s), parent organization, and affiliated organization(s); (8) an operations and maintenance plan which includes sufficient detail to support the budget estimate for operation and maintenance of the facilities; (9) assurances that the commitments and resources needed for proper operation and maintenance of the system are, and will continue to be, available, including the
46
qualifications of the organization and each individual associated with the proposed system; (10) for retail public utilities as defined by Texas Water Code (TWC), §13.002: (A) projected rate revenue from residential, commercial, and industrial customers; and (B) pro forma income, expense, and cash flow statements; (11) identification of any appropriate financial assurance, including those being offered to capital providers; (12) a notarized statement signed by the owner or responsible person that the business plan has been prepared under his direction and that he is responsible for the accuracy of the information; and (13) other information required by the executive director to determine the adequacy of the business plan or financial assurance. (g) Business plans not required. A person is not required to file a business plan if the person: (1) is a county; (2) is a retail public utility as defined by TWC, §13.002, unless that person is a utility as defined by that section; (3) has executed an agreement with a political subdivision to transfer the ownership and operation of the water supply system to the political subdivision; or (4) is a noncommunity nontransient water system and the person has demonstrated financial assurance under THSC, Chapter 361 or 382 or TWC, Chapter 26. (h) Beginning and completion of work. (1) No person may begin construction on a new public water system before receiving written approval of plans and specifications and, if required, approval of a business plan from the executive director. No person may begin construction of modifications to a public water system without providing notification to the executive director and submitting and receiving approval of plans and specifications if requested in accordance with subsection (j) of this section. (2) The executive director shall be notified in writing by the design engineer or the owner before construction is started. (3) Upon completion of the water works project, the engineer or owner shall notify the executive director in writing as to its completion and attest to the fact that the completed work is substantially in accordance with the plans and change orders on file with the commission. (i) Changes in plans and specifications. Any addenda or change orders which may involve a health hazard or relocation of facilities, such as wells, treatment units, and storage tanks, shall be submitted to the executive director for review and approval. (j) Changes in existing systems or supplies. Public water systems shall notify the executive director prior to making any significant change or addition to the system's production, treatment, storage, pressure maintenance, or distribution facilities. Public water systems shall submit plans and specifications for the proposed changes upon request. Changes to an existing disinfection process at a treatment plant that treats surface water or groundwater that is under the direct influence of surface water shall not be instituted without the prior approval of the executive director. (1) The following changes are considered to be significant:
47
(a) proposed changes to existing systems which result in an increase or decrease in production, treatment, storage, or pressure maintenance capacity;
(B) proposed changes to the disinfection process used at plants that treat surface water or groundwater that is under the direct influence of surface water including changes involving the disinfectants used, the disinfectant application points, or the disinfectant monitoring points; (C) proposed changes to the type of disinfectant used to maintain a disinfectant residual in the distribution system; (D) proposed changes in existing distribution systems when the change is greater than 10% of the existing distribution capacity or 250 connections, whichever is smaller, or results in the water system's inability to comply with any of the applicable capacity requirements of §290.45 of this title (relating to Minimum Water System Capacity Requirements); and (E) any other material changes specified by the executive director. (2) The executive director shall determine whether engineering plans and specifications will be required after reviewing the initial notification regarding the nature and extent of the modifications. (A) Upon request of the executive director, the water system shall submit plans and specifications in accordance with the requirements of subsection (d) of this section. (B) Unless plans and specifications are required by Chapter 293 of this title (relating to Water Districts), the executive director will not require another state agency or a political subdivision to submit planning material on distribution line improvements if the entity has its own internal review staff and complies with all of the following criteria: (i) the internal review staff includes one or more licensed professional engineers that are employed by the political subdivision and must be separate from, and not subject to the review or supervision of, the engineering staff or firm charged with the design of the distribution extension under review; (ii) a licensed professional engineer on the internal review staff determines and certifies in writing that the proposed distribution system changes comply with the requirements of §290.44 of this title (relating to Water Distribution) and will not result in a violation of any provision of §290.45 of this title; (iii) the state agency or political subdivision includes a copy of the written certification described in this subparagraph with the initial notice that is submitted to the executive director. (C) Unless plans and specifications are required by Chapter 293 of this title, the executive director will not require planning material on distribution line improvements from any public water system that is required to submit planning material to another state agency or political subdivision that complies with the requirements of subparagraph (B) of this paragraph. The notice to the executive director must include a statement that a state statute or local ordinance requires the planning materials to be submitted to the other state agency or political subdivision and a copy of the written certification that is required in subparagraph (B) of this paragraph. (3) If a certificate of convenience and necessity (CCN) is required or must be amended, the CCN application must be included with the notice to the executive director. (k) Planning material acceptance. Planning material for improvements to an existing system which does not meet the requirements of all sections of this subchapter will not be
48
considered unless the necessary modifications for correcting the deficiencies are included in the proposed improvements, or unless the executive director determines that reasonable progress is being made toward correcting the deficiencies and no immediate health hazard will be caused by the delay. (l) Exceptions. Requests for exceptions to one or more of the requirements in this subchapter shall be considered on an individual basis. Any water system which requests an exception must demonstrate to the satisfaction of the executive director that the exception will not compromise the public health or result in a degradation of service or water quality. (1) The exception must be requested in writing and must be substantiated by carefully documented data. The request for an exception shall precede the submission of engineering plans and specifications for a proposed project for which an exception is being requested. (2) Any exception granted by the commission is subject to revocation. (3) Any request for an exception which is not approved by the commission in writing is denied. (m) Notification of system startup or reactivation. The owner or responsible official must provide written notification to the commission of the startup of a new public water supply system or reactivation of an existing public water supply system. This notification must be made immediately upon meeting the definition of a public water system as defined in §290.38 of this title (relating to Definitions). (n) The commission may require the owner or operator of a public drinking water supply system that was constructed without the approval required by (THSC), §341.035, that has a history of noncompliance with (THSC), Chapter 341, Subchapter C or commission rules, or that is subject to a commission enforcement action to take the following action: (1) provide the executive director with a business plan that demonstrates that the system has available the financial, managerial, and technical resources adequate to ensure future operation of the system in accordance with applicable laws and rules. The business plan must fulfill all the requirements for a business plan as set forth in subsection (f) of this section; (2) provide adequate financial assurance of the ability to operate the system in accordance with applicable laws and rules. The executive director will set the amount of the financial assurance, after the business plan has been reviewed and approved by the executive director. (A) The amount of the financial assurance will equal the difference between the amount of projected system revenues and the projected cash needs for the period of time prescribed by the executive director. (B) The form of the financial assurance will be as specified in Chapter 37, Subchapter O of this title and will be as specified by the executive director. (C) If the executive director relies on rate increases or customer surcharges as the form of financial assurance, such funds shall be deposited in an escrow account as specified in Chapter 37, Subchapter O of this title and released only with the approval of the executive director. Source Note: The provisions of this §290.39 adopted to be effective October 1, 1992, 17 TexReg 6455; amended to be effective November 3, 1995, 20 TexReg 8620; amended to
49
be effective February 4, 1999, 24 TexReg 731; amended to be effective September 13, 2000, 25 TexReg 8880; amended to be effective May 16, 2002, 27 TexReg 4127; amended to be effective February 19, 2004, 29 TexReg 1373
50
Appendix B: Health Codes Excerpt from Texas Health and Safety Code § 341.036. SANITARY DEFECTS AT PUBLIC DRINKING WATER SUPPLY SYSTEMS. (a) A sanitary defect at a public drinking water supply system that obtains its water supply from underground sources shall be immediately corrected. (b) A public drinking water supply system furnishing drinking water from underground sources may not be established in a place subject to possible pollution by floodwaters unless the system is adequately protected against flooding. (c) Suction wells or suction pipes used in a public drinking water supply system must be constantly protected by practical safeguards against surface and subsurface pollution. (d) Livestock may not be permitted to enter or remain in the wellhouse enclosure of a public drinking water supply system. (e) Public drinking water distribution lines must be constructed of impervious materials with tight joints and must be a reasonably safe distance from sewer lines. (f) Water from a surface public drinking water supply may not be made accessible or delivered to a consumer for drinking purposes unless the water has been treated to make it safe for human consumption. Water treatment plants, including aeration, coagulation, mixing, settling, filtration, and chlorinating units, shall be of a size and type prescribed by good public health engineering practices. (g) A clear water reservoir shall be covered and be of a type and construction that prevents the entrance of dust, insects, and surface seepage. Acts 1989, 71st Leg., ch. 678, § 1, eff. Sept. 1, 1989. § 341.037. PROTECTION OF BODIES OF WATER FROM SEWAGE. The commission shall enforce state laws and take other necessary action to protect a spring, well, pond, lake, reservoir, or other stream in this state from any condition or pollution that results from sewage and that may endanger the public health. Acts 1989, 71st Leg., ch. 678, § 1, eff. Sept. 1, 1989. Amended by Acts 1995, 74th Leg., ch. 76, § 11.15, eff. Sept. 1, 1995. § 341.038. PROTECTION OF IMPOUNDED WATER FROM DISEASE-BEARING MOSQUITOES. A person that impounds water for public use shall cooperate with the commission and local departments of health to control disease-bearing mosquitoes on the impounded area. Acts 1989, 71st Leg., ch. 678, § 1, eff. Sept. 1, 1989. Amended by Acts 1995, 74th Leg., ch. 76, § 11.15, eff. Sept. 1, 1995.
51
§ 341.039. GRAYWATER STANDARDS. (a) The commission by rule shall adopt and implement minimum standards for the use and reuse of graywater for: (1) irrigation and other agricultural purposes; (2) domestic use, to the extent consistent with Subsection (c); (3) commercial purposes; and (4) industrial purposes. (b) The standards adopted by the commission under Subsection (a) must assure that the use of graywater is not a nuisance and does not damage the quality of surface water and groundwater in this state. (c) The commission may not require a permit for the domestic use of less than 400 gallons of graywater each day if the graywater: (1) originates from a private residence; (2) is used by the occupants of that residence for gardening, composting, or landscaping at the residence; (3) is collected using a system that overflows into a sewage collection or on-site wastewater treatment and disposal system; (4) is stored in tanks that: (A) are clearly labeled as nonpotable water; (B) restrict access, especially to children; and (C) eliminate habitat for mosquitoes and other vectors; (5) uses piping clearly identified as a nonpotable water conduit, including identification through the use of purple pipe, purple tape, or similar markings; (6) is generated without the formation of ponds or pools of graywater; (7) does not create runoff across the property lines or onto any paved surface; and (8) is distributed by a surface or subsurface system that does not spray into the air. (d) Each builder is encouraged to: (1) install plumbing in new housing in a manner that provides the capacity to collect graywater from all allowable sources; and (2) design and install a subsurface graywater system around the foundation of new housing in a way that minimizes foundation movement or cracking. (e) In this section, "graywater" means wastewater from clothes-washing machines, showers, bathtubs, hand-washing lavatories, and sinks that are not used for disposal of hazardous or toxic ingredients. The term does not include wastewater: (1) that has come in contact with toilet waste; (2) from the washing of material, including diapers, soiled with human excreta; or (3) from sinks used for food preparation or disposal. Acts 1989, 71st Leg., ch. 678, § 1, eff. Sept. 1, 1989. Amended by Acts 1993, 73rd Leg., ch. 233, § 2, eff. Aug. 30, 1993; Acts 1995, 74th Leg., ch. 76, § 11.16, eff. Sept. 1, 1995; Acts 2003, 78th Leg., ch. 689, § 2, eff. Sept. 1, 2003.
52
Appendix C: Seaholm Site Conditions Existing Conditions
Area Square
Feet Power Plant Upper Roof 21,845 Power Plant Lower Roof 13,310 Surface Parking / Circulation 109,400 Fuel Building Roof 1,185 Total Impervious Cover 145,740
Area/Volume Square
Feet Fuel Oil Tanks (estimated) 8,100Surge Tanks - South (estimated) 544
Area/Volume Cubic Feet
Surge Tanks - South (estimated) 7,616Fuel Oil Tanks (estimated) 283,500 Future Conditions
Area Square
Feet Power Plant Upper Roof 21,845 Power Plant Lower Roof 13,310 Fuel Building Roof 1,185 Roadways/Paving 61,990 Site Pedestrian Paving 25,395 North Plaza Pavers 64,534 South Terrace Pavers 19,180 Fountains 12,820 Office Roof (est.) 30,500 Residential Tower Roof (est.) 10,500 Total Impervious Cover (estimated) 261,259
53
Other Areas - Future Square
Feet Number Fountains 12,820 Landscaping (sod/ native plants) 65,248 Trees (not in landscape SF) 81
Land Use Square
Feet Seaholm - various uses See Above Fuel Building (Retail) 1,048 Retail 10,000 Residential 90,000 Commercial/Office 60,000 Parking ???
54
Appendix D: Texas Water Related Data
Figure 1. Average Monthly Evapotranspiration for Texas Cities
Figure 2. Plant Water Use Coefficients
55
Info
rmat
ion
prov
ided
, but
can
be
chan
ged
Info
rmat
ion
to b
e in
put b
y us
er
Out
puts
ETm
onth
ly *
Kc *
0.6
23
* A
lan
dsca
pe =
Ou
tdoo
r W
ater
Dem
and
Vol
um
e (g
allo
ns)
W
here
:
E
T mon
thly
= M
onth
ly E
vapo
trans
pira
tion
Am
ount
(inc
hes)
=
(g
iven
bel
ow fo
r Aus
tin)
K
c =
Pla
nt W
ater
Use
Coe
ffici
ent
=
0.5
(see
cha
rt)
0.75
0.
2
To
tal
(s.f.
)P
ortio
nof
Tot
al
A
land
scap
e =
Land
scap
e A
rea
6524
8 0.
7 =
4567
3.6
(med
ium
)
0.
2 =
1304
9.6
(hig
h)
0.1
= 65
24.8
(low
)
C
onve
rsio
n fro
m in
/ft^2
to
3 26.0
=
snol lag
ET-
Mon
thly
Eva
potra
nspi
ratio
n A
mou
nt fo
r Aus
tin, T
exas
(inc
hes)
Ja
nuar
y Fe
brua
ryM
arch
Apr
ilM
ayJu
neJu
lyA
ugus
tS
epte
mbe
rO
ctob
erN
ovem
ber
Dec
embe
rTo
tal
0.56
0.76
2.67
3.21
4.36
5.92
6.85
6.61
3.4
2.47
1.44
0.27
38.5
2
leg
end
Figu
re 3
. Pa
n E
vapo
ratio
n R
ates
56
Nee
ds o
f Lan
dsca
pe (g
allo
ns)
Janu
ary
Febr
uary
Mar
chA
pril
May
June
July
Aug
ust
Sep
tem
ber
Oct
ober
Nov
embe
rD
ecem
ber
Tota
l Nee
dsm
ediu
m79
6710
813
3798
745
670
6203
184
226
9745
794
043
4837
335
141
2048
738
4154
8037
high
3415
4634
1628
019
573
2658
536
097
4176
740
304
2073
115
061
8780
1646
2348
73
low
45
561
821
7126
1035
4548
1355
6953
7427
6420
0811
7122
031
316
tota
l11
837
1606
5 56
438
6785
2 92
161
1251
35
1447
94
1397
20
7186
8 52
210
3043
8 57
07
8142
26
Pan
Eva
pora
tion
Rat
es to
cal
cula
te lo
ss fr
om fo
unta
ins
(inch
es)
Janu
ary
Febr
uary
M
arch
Apr
il M
ay
June
July
A
ugus
tS
epte
mbe
rO
ctob
erN
ovem
ber
Dec
embe
rTo
tal
0.7
0.6
2.1
2.3
1.4
3.7
6.2
5.3
2.5
1.9
1.4
0.4
52.8
S
ize
of fo
unta
in b
ase
= 12
820
ft^2
co
nver
sion
=
0.62
3
w
ind
evap
. fac
tor
= 1.
2
Nee
ds (g
allo
ns)
Janu
ary
Febr
uary
M
arch
Apr
il M
ay
June
July
A
ugus
tS
epte
mbe
rO
ctob
erN
ovem
ber
Dec
embe
rTo
tal
6325
.657
50.5
1983
9.4
2242
7.1
1351
3.8
3584
5.0
5970
9.8
5089
2.3
2376
8.9
1859
3.4
1303
4.6
3737
.927
3438
.1
Figu
re 5
. Aus
tin, T
X P
an E
vapo
ratio
n R
ates
Figu
re 6
. L
ands
cape
Nee
ds
Jan
Fe
b M
ar
Apr
M
ay
June
Ju
ly
Aug
S
ept
Oct
N
ov
Dec
To
tal P
reci
p. O
ver 7
5 ye
ars
for a
Giv
en M
onth
14
9.56
158.
8113
4.04
191.
0127
9.41
247.
5617
0.73
169.
8123
9.58
224.
4719
5.26
166.
55 4747
4747
4757
5747
4747
5757
tnuoC M
onth
ly A
vg.
1.99
2.12
1.81
2.58
3.78
3.30
2.28
2.29
3.24
3.03
2.64
2.25
Mon
thly
Avg
. Per
cent
iles
1st (
100%
) 1.
992.
121.
812.
583.
783.
302.
282.
293.
243.
032.
642.
252n
d (7
5%)
1.50
1.59
1.36
1.94
2.83
2.48
1.71
1.72
2.43
2.28
1.98
1.69
3rd
(50%
) 1.
001.
060.
911.
291.
891.
651.
141.
151.
621.
521.
321.
134t
h (2
5%)
0.50
0.53
0.45
0.65
0.94
0.83
0.57
0.57
0.81
0.76
0.66
0.56
Figu
re 4
. Aus
tin, T
X A
vera
ge R
ainf
all D
Ata
57
Appendix E: Seaholm Demand Model
Provided below are descriptions of each water demand scenario examined, as well
as the models and the graphs necessary to evaluate them. Assuming that only non-
potable demands are considered, the following diagram explains the basic variables and
their affects on the model graphically:
Figure 1. Water Demand Scenario
We developed spreadsheet modeling to examine the varying scales of rainwater
collection. To further test our models, we developed four different design scenarios. The
four models of water demand can be described as follows:
• Scenario A – Irrigation with 30,000 gallons added storage
• Scenario B – Irrigation with office bldg and 60,000 gallons added storage
• Scenario C – Irrigation and fountains with 100,000 gallons added storage
• Scenario D – Irrigation, fountains, toilets w/100,000 gallons added storage
58
Scenario A : Irrigation with 30,000 gallons added storage
This scenario evaluated only the landscape irrigation demands when compared to
the volume of rainwater collected solely from the existing Seaholm Power Plant building
itself. Scenario A would require the least additional amount of equipment and of
maintenance. Minor renovations of the existing gutter systems would be necessary and
only approximately 30,000 to 35,000 gallons of additional storage tanks would be
needed. It was found that the rooftop area was insufficient to provide the capacity to
meet all of the landscape irrigation demands, though the system was able to satisfy
between 58% (fifty-eight) and 59% (fifty-nine) of the total demands. Also, due to the
increased demand and decreased supply in the summer months, the stored water level
fluctuated heavily. The demands also exceeded the amount of water stored and captured
between July and November, requiring additional use of municipal water, Figure 2.
Variable Notes Value
Total Rooftop Collection Area (s.f.) Power plant roof only 35,160
Total Cistern Capacity (gallons) Existing cistern + 30,000 gallons extra storage 87,000
Water Demands Evaluated (gallons per year) Landscape irrigation only 814,230
Percentage of Demands Met with Rainwater
In order to meet optimum system flow 58.5%
Total Rainwater Harvested (gallons per year) 476,320
Total Municipal Water Used (gallons per year) 337,900
Total Rainwater Spilled (gallons per year) 0
Figure 2. Scenario A: Results
59
Lan
dsca
pe w
ater
dem
ands
onl
y, e
xist
ing
pow
er p
lant
roo
f col
lect
ion
area
onl
y M
onth
La
ndsc
ape
Dem
ands
(G
allo
ns)
Tota
l D
eman
d M
et
(Gal
lons
)
Med
ian
Rai
nfal
l (In
ches
)
Rai
nfal
l C
olle
cted
(G
allo
ns)
Rai
nwat
er
Spill
ed
(Gal
lons
)
End-
of-M
onth
St
orag
e
(250
00 g
al. t
o st
art)
Mun
icip
al
Wat
er U
sed
(Gal
lons
)
25,0
00
Jan
11,8
37
6,92
5 1.
44
28,3
84
46
,460
4,
912
Feb
16,0
65
9,39
8 1.
90
37,4
52
74
,514
6,
667
Mar
56
,438
33
,016
1.
63
32,1
30
73
,627
23
,422
Apr
67
,852
39
,694
2.
06
40,6
06
74
,539
28
,159
May
92
,161
53
,914
3.
19
62,8
79
83
,505
38
,247
Jun
125,
135
73,2
04
2.36
46
,519
56,8
19
51,9
31
Jul
144,
794
84,7
04
1.27
25
,033
-2,8
52
60,0
89
Aug
13
9,72
0 81
,736
1.
59
31,3
41
-5
3,24
7 57
,984
Se
p 71
,868
42
,043
2.
82
55,5
86
-3
9,70
4 29
,825
O
ct
52,2
10
30,5
43
2.46
48
,490
-21,
757
21,6
67
Nov
30
,438
17
,806
1.
64
32,3
27
-7
,236
12
,632
D
ec
5,70
7 3,
339
1.81
35
,678
25,1
03
2,36
8
SU
MS
814,
226
476,
322
24.1
7
476,
425
0
337,
904
Figu
re 3
. Sc
enar
io A
: Wat
er D
eman
d M
odel
60
Scenario B: Irrigation with office bldg. and 60,000 gallons added storage
This scenario evaluated only the landscape irrigation demands when compared
with the rainwater collected from the existing Seaholm Power Plant building and to the
proposed office building. Scenario B would require a small amount of additional
equipment and maintenance than Scenario A. In addition to the minor renovations of the
existing gutter systems, a new gutter system and piping from the office building would be
necessary. Also, the increase in roof area requires the addition of approximately 60,000
gallons of additional storage tanks. It was determined that the increased rooftop area was
sufficient to provide capacity enough to meet all of the landscape irrigation demands
resulting in the rainwater satisfying 100% of the projected demands. However, the
rainwater collected exceeded the water demand and consequently, the tanks spilled
approximately 40,000 gallons between February and May, see Figure 4.
Variable Notes Value
Total Rooftop Collection Area (s.f.) Power plant & office roofs 65,660
Total Cistern Capacity (gallons) Existing cistern + 60,000 gallons extra storage 117,000
Water Demands Evaluated (gallons per year) Landscape irrigation only 814,230
Percentage of Demands Met with Rainwater
In order to meet optimum system flow 100%
Total Rainwater Harvested (gallons per year) 814,230
Total Municipal Water Used (gallons per year) 0
Total Rainwater Spilled (gallons per year) 39,870
Figure 4. Scenario B: Results
61
Lan
dsca
pe w
ater
dem
ands
onl
y, e
xist
ing
pow
er p
lant
& p
ropo
sed
offic
e ro
of c
olle
ctio
n ar
ea
Mon
th
Land
scap
e D
eman
ds
(Gal
lons
)
Tota
l D
eman
d M
et
(Gal
lons
)
Med
ian
Rai
nfal
l (In
ches
)
Rai
nfal
l C
olle
cted
(G
allo
ns)
Rai
nwat
er
Spill
ed
(Gal
lons
)
End-
of-M
onth
St
orag
e
(250
00 g
al. t
o st
art)
Mun
icip
al
Rai
nwat
er U
sed
(Gal
lons
)
25,0
00
Jan
11,8
37
11,8
37
1.44
53
,010
66,1
73
0
Feb
16,0
65
16,0
65
1.90
69
,944
3,
053
117,
000
0
Mar
56
,438
56
,438
1.
63
60,0
05
3,56
7 11
7,00
0 0
Apr
67,8
52
67,8
52
2.06
75
,834
7,
982
117,
000
0
May
92
,161
92
,161
3.
19
117,
433
25,2
72
117,
000
0
Jun
125,
135
125,
135
2.36
86
,878
78,7
43
0
Jul
144,
794
144,
794
1.27
46
,752
-19,
299
0
Aug
139,
720
139,
720
1.59
58
,532
-100
,487
0
Sep
71,8
68
71,8
68
2.82
10
3,81
2
-68,
543
0
Oct
52
,210
52
,210
2.
46
90,5
59
-3
0,19
4 0
Nov
30
,438
30
,438
1.
64
60,3
73
-2
59
0
Dec
5,
707
5,70
7 1.
81
66,6
31
60
,664
0
SUM
S 81
4,22
6 81
4,22
6 24
.17
88
9,76
4 39
,874
0
Figu
re 5
. Sc
enar
io B
: Wat
er D
eman
d M
odel
62
Scenario C: Irrigation and fountains with 100,000 gallons additional storage
This scenario evaluated the demands of landscape irrigation and of decorative
fountains when compared with the rainwater that could be collected from the existing
Seaholm Power Plant building in addition to the proposed office building. Scenario C
would require similar amounts of additional equipment and maintenance as in Scenario
B. Additional maintenance would also result in the use of the water to fill fountains,
which, because they in the public domain, must be more intensely filtered and tested.
The water capture area would also subsequently increase to approximately 100,000
gallons. It was determined that the additional rooftop area was still insufficient to
provide the capacity required to meet all of the outdoor water demands, though the
system was able to supply between 81% (eighty-one) and 82% (eighty-two) of the total
demands. The demands exceeded the amount of water captured and stored between July
and November, thus requiring the additional use of municipal water, Figure 6.
Variable Notes Value
Total Rooftop Collection Area (s.f.) Power plant & office roofs 65,660
Total Cistern Capacity (gallons) Existing cistern + 100,000 gallons extra storage 157,000
Water Demands Evaluated (gallons per year)
Landscape irrigation and fountain only 1,087,660
Percentage of Demands Met with Rainwater
In order to meet optimum system flow 81.8%
Total Rainwater Harvested (gallons per year) 889,710
Total Municipal Water Used (gallons per year) 197,960
Total Rainwater Spilled (gallons per year) 0
Figure 6. Scenario C: Results
63
Lan
dsca
pe &
Fou
ntai
n W
ater
Dem
ands
onl
y, e
xist
ing
pow
er p
lant
& p
ropo
sed
offic
e ro
of a
rea
Mon
th
Out
door
Wat
er
Dem
and
(Gal
lons
) To
tal
Dem
ands
(G
allo
ns)
Tota
l D
eman
d M
et b
y R
ainw
ater
(G
allo
ns)
Med
ian
Rai
nfal
l (In
ches
)
Rai
nfal
l C
olle
cted
(G
allo
ns)
Rai
nwat
er
Spill
ed
(gal
lons
)
End-
of-M
onth
St
orag
e
(250
00 g
al. t
o st
art)
Mun
icip
al
Rai
nwat
er
Use
d (G
allo
ns)
Fo
unta
in
Land
scap
e
25,0
00
Jan
6,32
6 11
,837
18
,163
14
,857
1.
44
53,0
10
63
,153
3,
306
Feb
5,75
1 16
,065
21
,815
17
,845
1.
90
69,9
44
11
5,25
3 3,
970
Mar
19
,839
56
,438
76
,277
62
,395
1.
63
60,0
05
11
2,86
3 13
,882
Apr
22,4
27
67,8
52
90,2
79
73,8
48
2.06
75
,834
114,
849
16,4
31
May
13
,514
92
,161
10
5,67
4 86
,442
3.
19
117,
433
14
5,84
0 19
,233
Jun
35,8
45
125,
135
160,
980
131,
682
2.36
86
,878
101,
036
29,2
98
Jul
59,7
10
144,
794
204,
503
167,
284
1.27
46
,752
-19,
496
37,2
20
Aug
50,8
92
139,
720
190,
613
155,
921
1.59
58
,532
-116
,885
34
,692
Sep
23,7
69
71,8
68
95,6
37
78,2
31
2.82
10
3,81
2
-91,
304
17,4
06
Oct
18
,593
52
,210
70
,804
57
,917
2.
46
90,5
59
-5
8,66
2 12
,886
Nov
13
,035
30
,438
43
,473
35
,561
1.
64
60,3
73
-3
3,85
0 7,
912
Dec
3,
738
5,70
7 9,
445
7,72
6 1.
81
66,6
31
25
,055
1,
719
SUM
S 27
3,43
8 81
4,22
6 1,
087,
664
889,
709
24.1
7
889,
764
0
197,
955
Figu
re 7
. Sc
enar
io C
: Wat
er D
eman
d M
odel
64
Scenario D: Irrigation, fountains, toilets with 100,000 gallons additional storage
This scenario evaluated the outdoor and the indoor water demands when
compared with the rainwater that could be collected from the both the existing Seaholm
Power Plant and the proposed office building. Scenario D would require the most
additional equipment and maintenance. The use of the rainwater to supplement the
demands for indoor water greatly increases the amount of required plumbing, which
inherently affects the cost of parts and labor. Storage capacity would need to expand to
approximately 100,000 gallons. It was found that the additional demands greatly reduced
the percentage of the system to meet its supply expectations between 36% (thirty-six) and
37% (thirty-seven). The demands exceeded the amount of water stored and captured
between August and October, thus requiring the additional use of municipal water, Figure
8.
Variable Notes Value
Total Rooftop Collection Area (s.f.) Power plant & office roofs 65,660
Total Cistern Capacity (gallons) Existing cistern + 100,000 gallons extra storage 107,000
Water Demands Evaluated (gallons) Landscape irrigation and fountain only 2,460,540
Percentage of Demands Met with Rainwater
In order to meet optimum system flow 36.1%
Total Rainwater Harvested (gallons per year) 888,260
Total Municipal Water Used (gallons per year) 1,572,290
Total Rainwater Spilled (gallons per year) 0
Figure 8. Scenario D: Results
65
Out
door
and
indo
or w
ater
dem
ands
, exi
stin
g po
wer
pla
nt &
pro
pose
d of
fice
roof
are
a M
onth
In
door
Wat
er
dem
and
(G
allo
ns)
Out
door
Wat
er
Dem
and
(Gal
lons
)
Tota
l D
eman
ds
(Gal
lons
)
Tota
l D
eman
d M
et
(Gal
lons
)
Med
ian
Rai
nfal
l (In
ches
)
Rai
nfal
l co
llect
ed
(Gal
lons
)
Rai
nwat
er
Spill
ed
(Gal
lons
)
End-
of-
mon
th
stor
age
(2
5000
gal
. to
star
t)
Mun
icip
al
Rai
nwat
er
Use
d (G
allo
ns)
O
ffice
R
etai
l Fo
unta
in
Land
scap
e
25,0
00
Jan
84,4
80
23,0
68
6,32
6 11
,837
12
5,71
1 45
,382
1.
44
53,0
10
32
,629
80
,329
Feb
84,4
80
20,8
36
5,75
1 16
,065
12
7,13
1 45
,894
1.
90
69,9
44
56
,679
81
,237
Mar
84
,480
23
,068
19
,839
56
,438
18
3,82
5 66
,361
1.
63
60,0
05
50
,323
11
7,46
4
Apr
84,4
80
22,3
24
22,4
27
67,8
52
197,
083
71,1
47
2.06
75
,834
55,0
10
125,
936
May
84
,480
23
,068
13
,514
92
,161
21
3,22
2 76
,973
3.
19
117,
433
95
,469
13
6,24
9
Jun
84,4
80
23,0
68
35,8
45
125,
135
268,
528
96,9
39
2.36
86
,878
85,4
09
171,
590
Jul
84,4
80
22,3
24
59,7
10
144,
794
311,
307
112,
382
1.27
46
,752
19,7
79
198,
925
Aug
84,4
80
23,0
68
50,8
92
139,
720
298,
161
107,
636
1.59
58
,532
-29,
325
190,
525
Sep
84,4
80
22,3
24
23,7
69
139,
720
270,
293
97,5
76
2.82
10
3,81
2
-23,
089
172,
717
Oct
84
,480
23
,068
18
,593
71
,868
19
8,01
0 71
,482
2.
46
90,5
59
-4
,011
12
6,52
8
Nov
84
,480
22
,324
13
,035
30
,438
15
0,27
7 54
,250
1.
64
60,3
73
2,
112
96,0
27
Dec
84
,480
23
,068
3,
738
5,70
7 11
6,99
3 42
,234
1.
81
66,6
31
26
,509
74
,759
SUM
S 1,
013,
760
271,
607
273,
438
901,
736
2,46
0,54
2 88
8,25
6 24
.17
88
9,76
4 0
1,
572,
286
Figu
re 9
. Sc
enar
io D
: W
ater
Dem
and
Mod
el
66
Appendix F: Stormwater Considerations at Seaholm
For site development, the City of Austin Drainage Criteria Manual requires that storm
water flow from a developed site “cannot exceed capacities of the existing downstream
drainage systems, or the predeveloped peak runoff rate of the site, whichever is less.”
Typically the reduction in peak runoff rate is achieved through the construction of a
storm water detention facility. In the case of the Seaholm site, collecting a portion of the
site’s precipitation essentially has the same runoff reduction effect as detention. By
reducing a portion of the site’s runoff volume through rainwater collection, the size and
therefore the cost of the developed site’s detention facility would be less due to the
supplemental rainwater collection.
Due to the large amount of impervious coverage contained in the plaza area, ample
evidence supports the generation of a considerable amount of storm water runoff from the
site. Capturing, storing, and reusing this water for either irrigation purposes either for the
indoor office facility use is imperative in order to mitigate the adverse impacts of the
excessive water that otherwise will be lost to evaporation. Primarily, water collected
from the site would be implemented in agricultural irrigation applications of the
landscape within and around the site. To achieve this, water runoff must be collected
from the plaza area and stored in the fuel tanks adjacent to the site. Traditional curb and
gutter drainage methods could be utilized in the project to divert storm water to storage
tanks (the City of Ann Arbor, Michigan, Website: http://www.ci.ann-arbor.mi.us).
A myriad of methods should be considered for the project to increase the infiltration
of water on site; to allow bio-remediation of pollutants by soils and plants; and to reduce
the storm water flow. Other factors that aid in the improvement of storm water quality are
the reduction of the amount of impervious surface, the collection and on-site storage of
storm water, and the increase in vegetation (the City of Ann Arbor, Michigan, Website:
http://www.ci.ann-arbor.mi.us). To mimic the functions of nature lost to urbanization,
natural options and onsite features can be used such as vegetated swales, as infiltration
67
trenches, and in bioretention. Structural means to hold storm water, such as rain barrels,
and to treat storm water should be considered and should be evaluated.
The integration of water conservation, of recycling, and of storm water collection,
storage and treatment, are all recommended strategies for the site (CABE Associates,
Inc., website: http://www.cabe.com/2000text.shtml) and it is important to generate site
plans for the plaza and the surrounding areas. Plans for the site should show adequate
grading and slopes, directions for the plaza and for the surrounding areas.
68
Appendix G: Radiance Scenarios
Low Consumption Scenario
An annual consumption pattern of houses with low-water demand was derived and
was used for developing models under this scenario. The average monthly water
consumption, aggregated annually, for such houses 2,057 gallons. However, significant
monthly variation was seen in the consumption pattern between summer & non-summer
months. Assuming that this difference was essentially associated with an increase in
outdoor expenditure of water for upkeep of the lawn and other landscape features, a
baseline indoor consumption demand was established based on consumption in the non-
summer months. The baseline indoor consumption level, as seen in Figure 1, was found
to be 1,690 gallons of water per month. Based on this information, an outdoor and an
indoor water demand pattern was established. Outdoor consumption is assumed to be all
values above the baseline value, and indoor consumption values at or below the baseline
level.
For a combined indoor &
outdoor low-water demand
pattern, the rain water system
was found to be effective in
meeting 88% (eighty-eight)
of all water demand, with a
collection area of 1600 sq. ft
(Appendix J). This model
was further tested for
efficiency with a larger
collection roof size; it was determined that with a roof size of 1850 sq. ft. or higher,
100% demand under this scenario was met.
0
500
1,000
1,500
2,000
2,500
3,000
3,500
1 2 3 4 5 6 7 8 9 10 11 12
Series1
Figure 1: Typical annual water consumption for low scenario
69
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
1 2 3 4 5 6 7 8 9 10 11 12
Series1
Figure 2. Typical annual water consumption for average scenario
For low consumption outdoor use only, it was seen that a 100% water demand was
met by the rain water system. Instead, under this scenario the consumption was so low
that there would be a very high amount of overflow and a very large cistern would be
needed to hold the monthly bourgeoning water residual. It was thus deemed that this
scenario was fairly impractical and ultimately infeasible, as displayed in Figure 1.
However, this model was analyzed further to check the proportion of indoor demand that
the model could meet, after meeting a 100% outdoor demand. It was seen that the rain
water system could meet 100% of outdoor demand and 85% (eighty-five) indoor demand
(Appendix J).
For low-consumption indoor use, it was again noted that 100% demand was satisfied
by the rainwater system. In summation, this system was deemed quite effective under the
low consumption scenario. The water demand for the given consumption pattern was met
almost entirely by rainwater alone. It was also concluded that a 6,000 gallon cistern
would suffice to hold the monthly residual generated by the rainwater system for indoor
and outdoor usage or outdoor only usage. An 8,000 gallon cistern is necessary to meet
storage needs for the indoor only scenario.
Average Consumption Scenario
An average annual consumption pattern of all houses within the Radiance subdivision
was calculated and used for
developing models under this
scenario. The average
monthly water consumption,
aggregated annually, for all
houses was observed to be
5,076 gallons. Again, the
significant monthly variation
in water consumption
between summer & non-
70
summer months was used to derive the outdoor & indoor water consumption pattern,
since it was inferred that this differential was essentially associated with an increase in
outdoor expenditure of water for lawn maintenance and for other landscape features. The
baseline indoor consumption level established using non-summer monthly consumption
was found to be 4,331 gallons of water per month. Based on this information, an outdoor
and indoor water demand pattern was established.
For a combined indoor & outdoor average water demand pattern, the rain water
system was found to be effective in meeting 35.5% of all water demand. The collection
area was again assumed to be a roof measuring 1,600 sq. ft. This model too was further
tested for efficiency with a larger collection roof size. It was found that with a roof size of
2,200 sq. ft., 48% of demand under this scenario was met by rainwater alone.
For average consumption outdoor use only, it was again seen that 100% water
demand was met by the rain water system. This model was further improvised to check
the proportion of indoor demand that the model could meet after meeting a 100% outdoor
demand. It was seen that the rain water system could meet a 100% outdoor demand and
23% indoor demand. The highest monthly water residual in the cistern was seen as 7,700
gallons. Hence this particular scenario needs a larger cistern capable of holding about
8,000 gallons of water.
For average consumption indoor use, it was noted that 43% (forty-three) of
demand was satisfied by the rainwater system. Summarizing, the rain water system can
effectively meet a significant portion of the water demand for the given average
consumption pattern. It was also observed that a cistern size of 7,000 gallons would
sufficiently hold the monthly residual generated by the rainwater system in the indoor
and outdoor combined water use scenario. A 5,000 gallon cistern is the appropriate size
cistern to accommodate residual for indoor only usage, while trying to store the residual
rainwater for the outdoor only scenario is unfeasible due to the rate of increasing
residual.
71
High Consumption Scenario
An annual utilization pattern of all high-water consumption houses within the
Radiance subdivision yielded the high water usage pattern used for developing models
under this scenario. The average monthly water consumption, aggregated annually, for
these high consumption houses was observed to be 10,514 gallons. Again, the significant
monthly variation in water consumption between summer & non-summer months was
used to derive the outdoor & indoor water consumption pattern, since, assumptively, this
difference was essentially associated with an outdoor expenditure increase of water for
upkeep of the lawn and for other landscape features. This difference was especially
pronounced in the high-consumption scenario. The baseline indoor consumption level
established using non-summer monthly consumption in this scenario was found to be
7,715 gallons of water per month. Again, based on this information, a high consumption
outdoor and indoor water demand pattern was established.
For the combined
indoor & outdoor high-
water demand pattern, the
rainwater system only
contributed to a mere 17%
(seventeen) of the
cumulative water demand.
The collection area was
again assumed to be a roof
measuring 1,600 sq. ft.
For high-consumption outdoor use only, the rainwater system only met 57% (fifty-
seven) of the total water demand. This indicates the wide disparity in the water
consumption pattern between high-consumption houses and the average Radiance house.
This model also observed a very high water residual in the early summer months. The
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
1 2 3 4 5 6 7 8 9 10 11 12
Series1
Figure 3. Typical average annual consumption in high scenario
72
system necessitates an 11,000 gallon cistern, which might make this scenario unfeasible,
see Figure 3.
For high-consumption indoor use pattern, it was noted that 25% (twenty-five) of the
demand was satisfied by the rainwater system. This model was further tested for
efficiency with a larger collection roof size. It was found that with a roof size of 2,200 sq.
ft. 34% (thirty-four) demand under this scenario was met by rainwater alone.
The rainwater system alone does not meet a significant portion of the water demand
for high consumption homes. However, for houses with bigger roof areas, a more
significant portion of the indoor water demand can be met by this system. It was also
observed that a cistern size of 6,000 gallons would sufficiently hold the monthly residual
generated by the rainwater system in the indoor water use scenario. The combined indoor
& outdoor water use would need approximately 8,000 gallons of capacity to hold the
necessary amount of water.
73
Appendix H: Radiance Systems Modeling
The following nine tables were generated using spreadsheet modeling to evaluate
three different levels of water consumption and three different modes of usage.
Assuming a pre-determined roof size, the consumption matrix yields nine different
combinations of rainwater and municipal water supply, offering a quantitative method to
determine both the practical and the economic feasibility of a rainwater system. In the
nine iterations that follow, the only variables that not fixed are the level of consumption
and the water usage pattern, whether inside, outside or both. Fixed variables include the
efficiency of the system, the size of the roof and the average amount of rainfall.
However, by changing the fixed and non-fixed variables, it becomes possible to use these
models to answer many of questions surrounding the implementation of a rainwater
system: roof size, necessary rainfall, etc.
1. Low Consumption
2. Average Consumption
3. High Consumption
A. Indoor & Outdoor Model 1A Model 2A Model 3A
B. Outdoor Only Model 1B Model 2B Model 3B
C. Indoor Only Model 1C Model 2C Model 3C
Figure 1. Consumption - Usage Matrix
74
Low Water Consumption:
Rainfall Collection - 90% collection, Low Demand, Indoor and Outdoor Usage
Month
Low Water demand
(indoor and outdoor)
Water demand from rainfall
(Indoor & outdoor)
Median Rainfall,
in.
Rainfall collected,
gal.
End-of-month
storage (Year 1)
End-of-month
storage (Year 2)
End-of-month
storage (Year 3)
% supplied by
municipal 0.12
Jan 2,056 1809.13 1.44 1291.85 4482.72 4444.66 4406.60
Feb 1,085 954.60 1.90 1704.53 5232.65 5194.59 5156.53
Mar 1,643 1445.99 1.63 1462.31 5248.97 5210.91 5172.85
Roof catchment area ,sq. ft.
1600
Apr 2,434 2142.14 2.06 1848.07 4954.90 4916.84 4878.78
May 3,186 2803.68 3.19 2861.81 5013.03 4974.97 4936.91
Jun 2,147 1889.21 2.36 2117.20 5241.02 5202.96 5164.90
Collection coefficent, gal/sq.ft/in.
0.623
Jul 2,213 1947.15 1.27 1139.34 4433.21 4395.15 4357.10
Aug 2,879 2533.23 1.59 1426.42 3326.41 3288.35 3250.29
Initial water stored, gal 5000
Sep 1,871 1646.48 2.82 2529.88 4209.81 4171.75 4133.69 Oct 1,906 1677.28 2.46 2206.92 4739.44 4701.38 4663.32 Nov 1,317 1158.96 1.64 1471.28 5051.76 5013.70 4975.64 Dec 1,947 1713.60 1.81 1623.79 4961.94 4923.88 4885.82
SUM 21721.45 24.17 21683.39
Figure 2. Model 1A
Rainfall Collection - 90% collection, Low Demand, Outdoor Usage Only
Month
Low Water demand
(outdoor)
Water demand from
rainfall (outdoor)
Median Rainfall,
in.
Rainfall collected,
gal.
End-of-month
storage (Year 1)
End-of-month
storage (Year 2)
End-of-month
storage (Year 3)
% supplied by
municipal 0
Jan 1802.44 1802.44 1.44 1291.85 4489.41 4376.62 4263.84
Feb 922.06 922.06 1.90 1704.53 5271.89 5159.10 5046.31
Mar 1396.69 1396.69 1.63 1462.31 5337.50 5224.71 5111.92
Roof catchment area ,sq. ft.
1600
Apr 2180.86 2180.86 2.06 1848.07 5004.71 4891.92 4779.13
May 2932.61 2932.61 3.19 2861.81 4933.92 4821.13 4708.34
Jun 1893.44 1893.44 2.36 2117.20 5157.68 5044.89 4932.10
Collection coefficent, gal/sq.ft/in.
0.623
Jul 1959.27 1959.27 1.27 1139.34 4337.75 4224.96 4112.17
Aug 2625.27 2625.27 1.59 1426.42 3138.90 3026.11 2913.32
Initial water stored, gal 5000
Sep 1617.61 1617.61 2.82 2529.88 4051.17 3938.38 3825.59 Oct 1652.61 1652.61 2.46 2206.92 4605.48 4492.69 4379.90 Nov 1119.45 1119.45 1.64 1471.28 4957.31 4844.52 4731.73 Dec 1693.88 1693.88 1.81 1623.79 4887.21 4774.42 4661.63
SUM 21796.18 24.17 21683.39
Figure 3. Model 1B
75
Low Water Consumption (cont.):
Rainfall Collection - 90% collection, Low Demand, Indoor Usage Only
Month
Low Water demand (indoor)
Water demand from
rainfall (Indoor)
Median Rainfall,
in.
Rainfall collected,
gal.
End-of-month
storage (Year 1)
End-of-month
storage (Year 2)
End-of-month
storage (Year 3)
% supplied by
municipal 0
Jan 1,689.29 1689.29 1.44 1291.85 102.56 2537.38 4972.20
Feb 1,084.77 1084.77 1.90 1704.53 722.32 3157.14 5591.96
Mar 1,643.17 1643.17 1.63 1462.31 541.46 2976.28 5411.09
Roof catchment area ,sq. ft.
1600
Apr 1,689.29 1689.29 2.06 1848.07 700.23 3135.05 5569.87
May 1,689.29 1689.29 3.19 2861.81 1872.75 4307.57 6742.39
Jun 1,689.29 1689.29 2.36 2117.20 2300.66 4735.48 7170.30
Collection coefficent, gal/sq.ft/in.
0.623
Jul 1,689.29 1689.29 1.27 1139.34 1750.71 4185.53 6620.35
Aug 1,689.29 1689.29 1.59 1426.42 1487.84 3922.66 6357.48
Initial water stored, gal 500
Sep 1,689.29 1689.29 2.82 2529.88 2328.43 4763.24 7198.06 Oct 1,689.29 1689.29 2.46 2206.92 2846.05 5280.87 7715.69 Nov 1,317.00 1317.00 1.64 1471.28 3000.32 5435.14 7869.96 Dec 1,689.29 1689.29 1.81 1623.79 2934.82 5369.64 7804.46
SUM 19248.57 24.17 21683.39
Figure 4. Model 1C
Average Water Consumption:
Rainfall Collection - 90% collection, Average Demand, Indoor and Outdoor Usage
Month
Water demand (indoor
and outdoor)
Water demand
from rainfall (Indoor & outdoor)
Median Rainfall,
in.
Rainfall collected,
gal.
End-of-month
storage (Year 1)
End-of-month
storage (Year 2)
End-of-month
storage (Year 3)
% supplied by
municipal 0.645
Jan 4,181 1484.26 1.44 1291.85 4807.60 4866.52 4925.44
Feb 3,631 1289.01 1.90 1704.53 5223.12 5282.04 5340.96
Mar 4,346 1542.83 1.63 1462.31 5142.60 5201.52 5260.44
Roof catchment area ,sq. ft.
1600
Apr 4,924 1748.02 2.06 1848.07 5242.64 5301.56 5360.48
May 5,461 1938.66 3.19 2861.81 6165.80 6224.72 6283.64
Jun 5,639 2001.85 2.36 2117.20 6281.16 6340.08 6399.00
Collection coefficent, gal/sq.ft/in.
0.623
Jul 6,531 2318.51 1.27 1139.34 5102.00 5160.92 5219.84
Aug 7,211 2559.91 1.59 1426.42 3968.51 4027.43 4086.35
Initial water stored, gal 5000
Sep 5,753 2042.32 2.82 2529.88 4456.08 4515.00 4573.92 Oct 4,815 1709.33 2.46 2206.92 4953.67 5012.59 5071.51 Nov 4,218 1497.39 1.64 1471.28 4927.55 4986.47 5045.39 Dec 4,204 1492.42 1.81 1623.79 5058.92 5117.84 5176.76
SUM 21624.47 24.17 21683.39
Figure 5. Model 2A
76
Average Water Consumption (cont.):
Rainfall Collection - 90% collection, Average Demand, Outdoor Usage Only
Month
Water demand
(outdoor)
Water demand
from rainfall (outdoor)
Median Rainfall,
in.
Rainfall collected,
gal.
End-of-month
storage (Year 1)
End-of-month
storage (Year 2)
End-of-month
storage (Year 3)
% supplied by
municipal 0
Jan 0 0.00 1.44 1291.85 3291.85 4915.64 16569.35
Feb 0 0.00 1.90 1704.53 3704.53 6620.17 18273.88
Mar 15 14.71 1.63 1462.31 3447.60 8067.76 19721.47
Roof catchment area ,sq. ft.
1600
Apr 593 592.71 2.06 1848.07 3255.36 9323.12 20976.83
May 1,130 1129.71 3.19 2861.81 3732.10 11055.22 22708.93
Jun 1,308 1307.71 2.36 2117.20 2809.49 11864.72 23518.43
Collection coefficent, gal/sq.ft/in.
0.623
Jul 2,200 2199.71 1.27 1139.34 939.63 10804.35 22458.06
Aug 2,880 2879.71 1.59 1426.42 546.71 9351.06 21004.77
Initial water stored, gal 2000
Sep 1,422 1421.71 2.82 2529.88 3108.17 10459.23 22112.94 Oct 484 483.71 2.46 2206.92 3723.21 12182.43 23836.14 Nov 0 0.00 1.64 1471.28 3471.28 13653.71 25307.42 Dec 0 0.00 1.81 1623.79 3623.79 15277.50 26931.21
SUM 10029.68 24.17 21683.39
Figure 6. Model 2B
Rainfall Collection - 90% collection, Average Demand, Indoor Usage Only
Month
Average Water
demand (indoor)
Water demand
from rainfall (Indoor)
Median Rainfall,
in.
Rainfall collected,
gal.
End-of-month
storage (Year 1)
End-of-month
storage (Year 2)
End-of-month
storage (Year 3)
% supplied by
municipal 0.57
Jan 4,181.00 1797.83 1.44 1291.85 3994.02 3797.16 3600.29 Feb 3,631.00 1561.33 1.90 1704.53 4137.22 3940.35 3743.49 Mar 4,331.29 1862.45 1.63 1462.31 3737.07 3540.20 3343.34
Roof catchment area ,sq. ft.
1600
Apr 4,331.29 1862.45 2.06 1848.07 3722.68 3525.82 3328.95 May 4,331.29 1862.45 3.19 2861.81 4722.04 4525.18 4328.31 Jun 4,331.29 1862.45 2.36 2117.20 4976.79 4779.92 4583.06
Collection coefficent, gal/sq.ft/in.
0.623
Jul 4,331.29 1862.45 1.27 1139.34 4253.68 4056.81 3859.94 Aug 4,331.29 1862.45 1.59 1426.42 3817.64 3620.78 3423.91
Initial water stored, gal 4500
Sep 4,331.29 1862.45 2.82 2529.88 4485.07 4288.20 4091.33 Oct 4,331.29 1862.45 2.46 2206.92 4829.53 4632.66 4435.79 Nov 4,218.00 1813.74 1.64 1471.28 4487.07 4290.20 4093.33 Dec 4,204.00 1807.72 1.81 1623.79 4303.13 4106.27 3909.40
SUM 21880.26 24.17 21683.39
Figure 7. Model 2C
77
High Water Consumption:
Rainfall Collection - 90% collection, High Demand, Indoor and Outdoor Usage
Month
High Water demand
(indoor and outdoor)
Water demand from
rainfall (Indoor & outdoor)
Median Rainfall,
in.
Rainfall collected,
gal.
End-of-month
storage (Year 1)
End-of-month
storage (Year 2)
End-of-month
storage (Year 3)
% supplied by
municipal 0.83
Jan 6,426.42 1092.49 1.44 1291.85 5199.36 5434.95 5670.55
Feb 5,982.33 1017.00 1.90 1704.53 5886.89 6122.49 6358.08
Mar 7,326.67 1245.53 1.63 1462.31 6103.67 6339.26 6574.85
Roof catchment area ,sq. ft.
1600
Apr 9,769.67 1660.84 2.06 1848.07 6290.89 6526.48 6762.07
May 11,649.67 1980.44 3.19 2861.81 7172.26 7407.85 7643.44
Jun 13,175.00 2239.75 2.36 2117.20 7049.71 7285.30 7520.90
Collection coefficent, gal/sq.ft/in.
0.623
Jul 16,391.00 2786.47 1.27 1139.34 5402.58 5638.18 5873.77
Aug 17,901.00 3043.17 1.59 1426.42 3785.84 4021.43 4257.02
Initial water stored, gal 5000
Sep 13,039.37 2216.69 2.82 2529.88 4099.02 4334.61 4570.21 Oct 9,958.40 1692.93 2.46 2206.92 4613.01 4848.60 5084.19 Nov 7,967.20 1354.42 1.64 1471.28 4729.86 4965.45 5201.05 Dec 6,576.80 1118.06 1.81 1623.79 5235.59 5471.19 5706.78
SUM 21447.80 24.17 21683.39
Figure 8. Model 1C
Rainfall Collection - 90% collection, High Demand, Outdoor Usage Only
Month
High Water demand
(outdoor)
Water demand from
rainfall (outdoor)
Median Rainfall,
in.
Rainfall collected,
gal.
End-of-month
storage (Year 1)
End-of-month
storage (Year 2)
End-of-month
storage (Year 3)
% supplied by
municipal 0.43
Jan 0.00 0.00 1.44 1291.85 6291.85 6242.02 6192.19
Feb 0.00 0.00 1.90 1704.53 7996.38 7946.55 7896.72
Mar 0.00 0.00 1.63 1462.31 9458.69 9408.85 9359.02
Roof catchment area ,sq. ft.
1600
Apr 2,054.31 1170.96 2.06 1848.07 10135.80 10085.96 10036.13
May 3,934.31 2242.56 3.19 2861.81 10755.05 10705.22 10655.39
Jun 5,459.65 3112.00 2.36 2117.20 9760.26 9710.42 9660.59
Collection coefficent, gal/sq.ft/in.
0.623
Jul 8,675.65 4945.12 1.27 1139.34 5954.48 5904.65 5854.82
Aug 10,185.65 5805.82 1.59 1426.42 1575.08 1525.25 1475.42
Initial water stored, gal 5000
Sep 5,324.01 3034.69 2.82 2529.88 1070.28 1020.44 970.61 Oct 2,243.05 1278.54 2.46 2206.92 1998.65 1948.82 1898.99 Nov 251.85 143.55 1.64 1471.28 3326.38 3276.55 3226.71 Dec 0.00 0.00 1.81 1623.79 4950.17 4900.33 4850.50
SUM 21733.22 24.17 21683.39
Figure 9. Model 2C
78
High Water Consumption (con’t):
Rainfall Collection - 90% collection, High Demand, Indoor Usage Only
Month
High Water demand (indoor)
Water demand from
rainfall (Indoor)
Median Rainfall,
in.
Rainfall collected,
gal.
End-of-month
storage (Year 1)
End-of-month
storage (Year 2)
End-of-month
storage (Year 3)
% supplied by municipal 0.75
Jan 6,426.42 1606.60 1.44 1291.85 4685.25 4359.88 4034.50
Feb 5,982.33 1495.58 1.90 1704.53 4894.19 4568.82 4243.45
Mar 7,326.67 1831.67 1.63 1462.31 4524.83 4199.46 3874.09
Roof catchment area ,sq. ft.
1600
Apr 7,715.35 1928.84 2.06 1848.07 4444.06 4118.69 3793.31
May 7,715.35 1928.84 3.19 2861.81 5377.03 5051.66 4726.29
Jun 7,715.35 1928.84 2.36 2117.20 5565.40 5240.03 4914.65
Collection coefficent, gal/sq.ft/in.
0.623
Jul 7,715.35 1928.84 1.27 1139.34 4775.90 4450.53 4125.16
Aug 7,715.35 1928.84 1.59 1426.42 4273.49 3948.11 3622.74
Initial water stored, gal 5000
Sep 7,715.35 1928.84 2.82 2529.88 4874.52 4549.15 4223.78 Oct 7,715.35 1928.84 2.46 2206.92 5152.60 4827.23 4501.85 Nov 7,715.35 1928.84 1.64 1471.28 4695.04 4369.67 4044.29 Dec 6,576.80 1644.20 1.81 1623.79 4674.63 4349.25 4023.88
SUM 22008.76 24.17 21683.39
Figure 10. Model 3C
79
Appendix I: Economic Analysis
Implementation of Individual Rainwater Harvesting System
This section will provide all of the figures that were created to analyze the cost of
implementing rainwater collection systems on individual systems. Please see the
description in the report for background information on the boundaries of this analysis.
Figures 1 thru 9 show the economic feasibility of the nine permutations of rainwater
system uses, of users and of roof size.
Cost Analysis: Low Consumption, Indoor & Outdoor
$-
$5,000.00
$10,000.00
$15,000.00
$20,000.00
$25,000.00
$30,000.00
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
Time (Yrs.)
Cum
ulat
ive
Cos
t ($)
Costs
Savings
Figure 1. Cost Analysis of Low Consumption Household for Indoor and Outdoor Use
80
Cost Analysis: Low Consumption, Outdoor Only
$-
$2,000.00
$4,000.00
$6,000.00
$8,000.00
$10,000.00
$12,000.00
$14,000.00
$16,000.00
$18,000.00
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
Time (Yrs.)
Cum
ulat
ive
Cos
t ($)
Costs
Savings
Figure 2. Cost Analysis of Low Consumption Household for Outdoor Use
Cost Analysis: Low Consumption, Indoor & Outdoor, Large Roof
$-
$5,000.00
$10,000.00
$15,000.00
$20,000.00
$25,000.00
$30,000.00
$35,000.00
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
Time (Yrs.)
Cum
ulat
ive
Cos
t ($)
Costs
Savings
Figure 3. Cost Analysis of Low Consumption Household for Indoor and Outdoor Use with Large Roof
81
Cost Analysis: Medium Consumption, Indoor & Outdoor
$-
$5,000.00
$10,000.00
$15,000.00
$20,000.00
$25,000.00
$30,000.00
$35,000.00
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
Time (Yrs.)
Cum
ulat
ive
Cos
t ($)
Costs
Savings
Figure 4. Cost Analysis of Medium Consumption Household for Indoor and Outdoor Use
Cost Analysis: Medium Consumption, Outdoor Only
$-
$2,000.00
$4,000.00
$6,000.00
$8,000.00
$10,000.00
$12,000.00
$14,000.00
$16,000.00
$18,000.00
$20,000.00
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
Time (Yrs.)
Cum
ulat
ive
Cos
t ($)
Costs
Savings
Figure 5. Cost Analysis of Medium Consumption Household Outdoor Use
82
Cost Analysis: Medium Consumption, Indoor & Outdoor, Large Roof
$-
$5,000.00
$10,000.00
$15,000.00
$20,000.00
$25,000.00
$30,000.00
$35,000.00
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
Time (Yrs.)
Cum
ulat
ive
Cos
t ($)
Costs
Savings
Figure 6. Cost Analysis of Medium Consumption Household for Indoor and Outdoor Use with Large Roof
Cost Analysis: High Consumption, Indoor & Outdoor
$-
$5,000.00
$10,000.00
$15,000.00
$20,000.00
$25,000.00
$30,000.00
$35,000.00
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
Time (Yrs.)
Cum
ulat
ive
Cos
t ($)
Costs
Savings
Figure 7. Cost Analysis of High Consumption Household for Indoor and Outdoor Use
83
Cost Analysis: High Consumption, Outdoor Only
$-
$2,000.00
$4,000.00
$6,000.00
$8,000.00
$10,000.00
$12,000.00
$14,000.00
$16,000.00
$18,000.00
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
Time (Yrs.)
Cum
ulat
ive
Cos
t ($)
Costs
Savings
Figure 8. Cost Analysis of High Consumption Household Outdoor Use
Cost Analysis: High Consumption, Indoor & Outdoor, Large Roof
$-
$5,000.00
$10,000.00
$15,000.00
$20,000.00
$25,000.00
$30,000.00
$35,000.00
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
Time (Yrs.)
Cum
ulat
ive
Cos
t ($)
Costs
Savings
Figure 9. Cost Analysis of High Consumption Household for Indoor and Outdoor Use with Large Roof
84
Appendix J: Notes on Cost Analysis and Cisterns
The costs of the various pieces of equipment needed for residential rainwater
collection were obtained from several websites. Tank Town, a major local supplier of
rainwater collection equipment has a catalog listing prices and descriptions for the
various types of equipment they sell for installing rainwater collection systems
(http://rainwater.org/catalog.pdf). Their catalog was used as the main source for pricing
with verification and supplemental information, especially for different types of storage
tanks, found in The Texas Manual on Rainwater Harvesting and the RS Means 2005
Building Construction Cost Data guidebook. As a slight offset to the cost of the
rainwater collection system, Hays County offers a $100 rebate for rainwater collection
systems as well as property tax exemption on the value of the system. The rebate has
already been included in the economic model.
The major expense of a
rainwater collection system is the
storage tank. The size of the storage
tank determines the reliability of the
collection system as a source of water
between rainfall events. The size of
the tank also has a very significant
impact on the cost of the system and
therefore its economic feasibility when
compared to municipal water supply.
The tables shown below summarize
the cost of various types and sizes of
storage tanks, which can then be used
as an input to the economic model to
compare how various storage tank
options affect the cost and economic
feasibility of the system.
Figure 1. Fiberglass Tank Costs. Source: Tank Town2004 Catalog (http://rainwater.org/catalog.pdf)
85
Figure 3: Estimated Tank Costs
Figure 2. Cisterns
86
Appendix K: Cost Analysis and Monthly Savings
Below are three sets of examples of the models designed to quantitatively analyze
various design scenarios considered for the residential developments in the Radiance
Community. These tables and their underlying models resulted in the graphs examined in
Appendix I. These models can be have been designed to allow rainwater systems to be
evaluated for any combination of variables and are available from the University of
Texas.
Low Consumption Square Feet 1600 Ave. monthly water bill savings $ 9.05 Installation Factor 15% Replacement Replacement
Item Cost/Unit Total Intervals (years) Cost Roof washer $ 850.00 $ 850.00 50 N/A Tank (10,000g) $ 4,290.00 $ 4,290.00 50 N/A Pump $ 585.00 $ 585.00 8 $ 585.00 Filter assembly $ 325.00 $ 325.00 50 N/A 3 & 5 micron filter* $ 100.00 $ 100.00 1 $ 100.00 UV light $ 675.00 $ 675.00 1.2 $ 80.00 Piping $ 3.00 $ 150.00 50 N/A Electricity $ 0.07 $ 25.55 N/A N/A * 1 year is a pack (12) 5 micrion filters and (4) 3 micron filters
Figure 1. Monthly Savings
Low Consumption (6000 gal.) Outdoor Only Indoor & Outdoor Large Roof Roof washer $ 850.00 $ 850.00 Tank $ 4,290.00 $ 4,290.00 Pump $ 585.00 $ 585.00 Filter assembly $ 325.00 3 & 5 micron filter* $ 100.00 UV light $ 675.00 Total Cost $ 5,725.00 $ 6,825.00 same Total water consumption 2057 2057 2057 Rainwater consumption 367 1810 2057 Well water consumption 1690 247 0 $ 1.84 $ 9.05 $ 10.29 $ 22.00 Total Monthly Savings $ 1.84 $ 9.05 $ 32.29
Figure 2. System Cost
87
Medium Consumption Square Feet 1600 Ave. monthly water bill savings $ 10.82 Installation Factor 15% Replacement Replacement
Item Cost/Unit Total Intervals (years) Cost Roof washer $ 850.00 $ 850.00 50 N/A Tank (20,000g) $ 4,685.00 $ 4,685.00 50 N/A Pump $ 585.00 $ 585.00 8 $ 585.00 Filter assembly $ 325.00 $ 325.00 50 N/A 3 & 5 micron filter* $ 100.00 $ 100.00 1 $ 100.00 UV light $ 675.00 $ 675.00 1.2 $ 80.00 Piping $ 3.00 $ 150.00 50 N/A Electricity $ 0.07 $ 51.10 N/A N/A * 1 year is a pack (12) 5 micrion filters and (4) 3 micron filters
Figure 3. Monthly Savings
Med Consumption (8000 gal.) Outdoor Only Indoor & Outdoor Large Roof Roof washer $ 850.00 $ 850.00 Tank $ 4,685.00 $ 4,685.00 Pump $ 585.00 $ 585.00 Filter assembly $ 325.00 3 & 5 micron filter* $ 100.00 UV light $ 675.00 Total Cost $ 6,120.00 $ 7,220.00 same Total water consumption 5076 5076 5076 Rainwater consumption 745 1802 2436 Well water consumption 4331 3274 2640 $ 4.47 $ 10.82 $ 14.26 Total Monthly Savings $ 4.47 $ 10.82 $ 14.26
Figure 4. System Cost
88
High Consumption Square Feet 1600 Ave. monthly water bill savings $ 12.51 Installation Factor 15% Replacement Replacement
Item Cost/Unit Total Intervals (years) Cost Roof washer $ 850.00 $ 850.00 50 $ 850.00 Tank (20,000g) $ 5,625.00 $ 5,625.00 50 N/A Pump $ 585.00 $ 585.00 8 $ 585.00 Filter assembly $ 325.00 $ 325.00 50 N/A 3 & 5 micron filter* $ 100.00 $ 100.00 1 $ 100.00 UV light $ 675.00 $ 675.00 1.2 $ 80.00 Piping $ 3.00 $ 150.00 50 N/A Electricity $ 0.07 $ 76.65 N/A N/A* 1 year is a pack (12) 5 micrion filters and (4) 3 micron filters
Figure 5. Monthly Savings
High Consumption (11,000 gal.) Outdoor Only Indoor & Outdoor Large Roof Roof washer $ 850.00 $ 850.00 Tank $ 5,625.00 $ 5,625.00 Pump $ 585.00 $ 585.00 Filter assembly $ 325.00 3 & 5 micron filter* $ 100.00 UV light $ 675.00 Total Cost $ 7,060.00 $ 8,160.00 same Total water consumption 10514 10514 10514Rainwater consumption 1595 1787 2623Well water consumption 8919 8727 7891 $ 11.17 $ 12.51 $ 18.36 Total Monthly Savings $ 11.17 $ 12.51 $ 18.36
Figure 6. System Cost
89
Appendix L: Seaholm Cost Analysis
To complement the demand models in Appendix D, additional spreadsheet
models were created to allow for variations in the cost of the systems. The models
presented below illustrate the same four scenarios and can be used in conjunction with
the Seaholm demand Models to create a complete picture of the costs associated with
rainwater harvesting.
• Scenario A – Irrigation with 30,000 gallons added storage
• Scenario B – Irrigation with office bldg and 60,000 gallons added storage
• Scenario C – Irrigation and fountains with 100,000 gallons added storage
• Scenario D – Irrigation, fountains, toilets w/100,000 gallons added storage
Scenario A - Existing System, Additional Storage Add. Stor Vol (Gal) 30,000 Replacement Total
Item Cost/Unit Total Intervals (years) Cost Tank $ 12,000.00 2 50 $ 24,000.00 Filtration System $ 1,000.00 1 50 $ 1,000.00 Pump $ 1,000.00 2 8 $ 2,000.00 Connection* $ 1,000.00 1 $ 1,000.00 Piping $ 8.45 200 25 $ 1,690.00 Maintenance $ 50.00 12 50 $ 600.00 *to municipal water service + bkflw prev, etc Rainwater Collected 476.3 Water Rate $ 3.50 Yearly Savings $ 1,667.05
Figure 1. Scenario A: Cost Analysis
90
Scenario B - Additional Storage, Office Bldg Collection Add. Stor Vol (Gal) 60,000 Replacement Total
Item Cost/Unit Total Intervals (years) Cost Tank $ 16,500.00 3 50 $ 49,500.00 Filtration System $ 1,000.00 2 50 $ 2,000.00 Pump $ 1,000.00 3 8 $ 3,000.00 Connection* $ 1,000.00 1 50 $ 1,000.00 Piping $ 8.45 400 25 $ 3,380.00 Maintenance $ 50.00 12 50 $ 600.00 *to municipal water service + bkflw prev, etc Rainwater Collected 814.2 Water Rate $ 3.50 Yearly Savings $ 2,849.70
Figure 2. Scenario B: Cost Analysis
Scenario C - Irrigation + Fountains Add. Stor Vol (Gal) 100,000 Replacement Total
Item Cost/Unit Total Intervals (years) Cost Tank $ 16,500.00 5 50 $ 82,500.00 Filtration System $ 1,000.00 2 50 $ 2,000.00 Pump $ 750.00 4 8 $ 3,000.00 Connection* $ 1,000.00 1 50 $ 1,000.00 Exterior Piping $ 8.45 600 25 $ 5,070.00 Maintenance $ 50.00 12 50 $ 600.00 *to municipal water service + bkflw prev, etc Rainwater Collected 889.7 Water Rate $ 3.50 Yearly Savings $ 3,113.95
Figure 3. Scenario C: Cost Analysis
91
Scenario D - Irrigation + Fountains + Flushing Add. Stor Vol (Gal) 100,000 Office Building Size (sf) 100,000 Replacement Total
Item Cost/Unit Total Intervals (years) Cost Tank $ 16,500.00 5 50 $ 82,500.00 Filtration System $ 1,000.00 2 50 $ 2,000.00 Pump $ 1,000.00 6 8 $ 6,000.00 Connection* $ 1,000.00 1 50 $ 1,000.00 Exterior Piping $ 8.45 600 25 $ 5,070.00 Interior Piping $ 0.06 100000 50 $ 6,000.00 Maintenance $ 80.00 12 50 $ 960.00 *to municipal water service + bkflw prev, etc Rainwater Collected 889.7 Water Rate $ 3.50 Yearly Savings $ 3,113.95
Figure 4. Scenario D: Cost Analysis
92
Works Cited and Referenced
Butler, Kent & Andrew Karvonen. Integrative Water Management and Conservation
Development: Alternatives for the Central Texas Hill Country. University of Texas at
Austin. Dec 2004
Embid, A. The transfer from the Ebro basin to the Mediterranean basins as a decision on
the 2001 National Hydrological Plan: the main problems posed. 2003. International
Journal of Water Resources Development 19: 399-411.
Gelt, Joe. Home Use of Graywater, Rainwater Conserves Water--and May Save Money.
09 Nov 2005. (http://ag.arizona.edu/AZWATER/arroyo/071rain.html).
General Rainwater Harvesting Technologies. United Nations Environment Program:
Newletter and Technical Publications: Sourcebook of Alternative Technologies for
Freshwater Augmentation in some Countries in Asia. 05 Nov 2005
(http://www.unep.or.jp/ietc/publications/techpublications/techpub-8e/rainwater2.asp).
Grainger Products Webpage. W.W. Grainger, Inc. 01 Dec. 2005.
(http://www.grainger.com/Grainger/wwg/start.shtml).
Health and Safety Code. 06 Oct 2005. Texas Department of State Health Services. 12
Nov 2005.
Home water Treatment Devices. NSF Consumer Information. 10 Nov 2005.
(http://www.nsf.org/consumer/drinking_water/dw_treatment.asp?program=WaterTre#tre
atment).
Hunter Industries. Irrigation Products Catalog. San Marcos, CA: Hunter Industries.
1999.
93
An Introduction to Rainwater Harvesting. Urban Water Resources Management. 05 Nov
2005. (http://www.gdrc.org/uem/water/rainwater/introduction.html).
Krishna, Hari J. Rainwater Harvesting in Texas. Texas Water Development Board. 15
Nov 2005. (www.twdb.state.texas.us).
Krishna, Hari J., et al. The Texas Manual on Rainwater Harvesting. Third Edition. 2005.
Texas Water Development Board. 4 Nov 2005
(http://www.twdb.state.tx.us/publications/reports/RainwaterHarvestingManual_3rdedi
tion.pdf).
Muhammad Mizanur Rahaman & Olli Varis. Integrated water resources management:
evolution, prospects and future challenges. Spring 2005. Sustainability: Science,
Practice, & Policy. (http://ejournal.nbii.org).
Novak, Shonda. “Seaholm’s Rebirth Set For 2008.” Austin American Statesman 17
January 2006. 10 July 2006 <http://www.statesman.com/news/content/business/
stories/realestate/01/18seaholm.html>
R.S. Means Company. Building Construction Cost Data. Kingston, MA : R.S. Means
Co. 2005.
Rainwater Harvesting. City of Austin – Green Building Program Factsheet. City of
Austin. 4 Nov 2005. (http://www.ci.austin.tx.us/greenbuilder/fs_rainharvest.htm).
Rules and Guidance for Public Drinking Water. 12 July 2004. Texas Commission of
Environmental Quality. 12 Nov 2005.
(http://www.tceq.state.tx.us/permitting/water_supply/pdw/pdw_rulesGuide.html).
94
“Seaholm Power, LLC.” Southwest Strategies Group, Inc. 2004. Seaholm Power, LLC.
15 Dec 2005. (http://www.seaholm.info)
Smet, Jo. Domestic Rainwater Harvesting: Well Fact Sheet. March 2003 Lboro, UK. 05
Nov 2005. (http://www.lboro.ac.uk/well/resources/fact-sheets/fact-sheets-
htm/drh.htm)
The 2004 Tank Town Catalog of Rainwater Collection Stuff. Tank Town. 4 Nov 2005
(http://rainwater.org/catalog.pdf).
Texas A & M Rainwater Harvesting Webpage. Texas A & M University. 6 Nov 2005
(http://rainwaterharvesting.tamu.edu/complex.html)
Texas Administrative Code. 6 June 1996. Texas Secretary of State. 12 Nov 2005
(http://info.sos.state.tx.us/pls/pub/readtac$ext.ViewTAC?tac_view=5&ti=30&pt=1&c
h=290&sch=D&rl=Y).
Texas Guide to Rainwater Harvesting – Second Edition. June 1997. Texas Water
Development Board. 05 Nov 2005.
(http://www.ircsa.org/factsheets/TexasRainHarv.pdf).
Texas Manual on Rainwater Harvesting – Third Edition. June 2005. Texas Water
Development Board. 05 Nov 2005.
(http://www.twdb.state.tx.us/publications/reports/RainwaterHarvestingManual_3rdedi
tion.pdf).
Texas Utilities Criteria Manual. June 2002. City of Austin. 05 Nov 2005.
(http://www.amlegal.com/austin_nxt2/gateway.dll?f=templates&fn=default.htm&vid
=amlegal:austin_utilities).
95
United Nations Environment Program, Division of Technology, Industry, and Economics.
United Nations. 11 Oct 2005.
(http://www.unep.or.jp/ietc/publications/techpublications/techpub-8e/rainwater2.asp).
Waskom, R. Graywater Reuse and Rainwater Harvesting. Colorado State University,
Cooperative Extension – Natural Resources. 08 Nov 2005.
(http://www.ext.colostate.edu/PUBS/natres/06702.html)
Water Quality Products. Health Goods. 10 Nov 2005.
(http://www.healthgoods.com/Shopping/Water_Quality_Products/National_Drinking
_Water_Standards2.htm).
96
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