harvesting, storing and treating rainwater

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Harvesting, Storing, and Treating

Rainwater for Domestic Indoor Use

Texas Commission on Environmental Quality

(GI-366) Jan. 2007


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Published and distributed by theTexas Commission on Environmental Quality

P. O. Box 13087Austin, TX 78711-3087

Kathleen Hartnett White, Chairman

Larry R. Soward, Commissioner

Glenn Shankle, Executive Director

We authorize you to use any original material contained in this publicationthat is, any material

we did not obtain rom other sources. Please acknowledge the TCEQ as your source.

Copies o this publication are available or public use through the Texas State Library, other state

depository libraries, and the TCEQ Library, in compliance with state depository law. For more

inormation on TCEQ publications call 512-239-0028 or visit our web site at:

www.tceq.state.tx.us/publications

The TCEQ is an equal opportunity/armative action employer. The agency does not allow discrimination on the basis o race, color,religion, national origin, sex, disability, age, sexual orientation or veteran status. In compliance with the Americans with Disabilities

Act, this document may be requested in alternate ormats by contacting the TCEQ at 512-239-0028, Fax 512-239-4488, or1-800-RELAY-TX (TDD), or by writing P.O. Box 13087, Austin, TX 78711-3087.
http://www.tceq.state.tx.us/publicationshttp://www.tceq.state.tx.us/publications


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Table of Contents

PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

CHAPTER 1. INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Purpose and Organization o This Document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Summary o This Guidance Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

What Kinds o Contaminants Can Be Found in Rainwater? . . . . . . . . . . . . . . . . . . . . . . . . . 3Debris . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Chemical Contaminants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Volatile Organic Chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Synthetic Organic Chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Microbiological Contaminants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Product Certifcations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Technical and Proessional Assistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Droughts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

CHAPTER 2. COLLECTION AND STORAGE OF UNTREATED RAINWATER . . . . . . . 9

Roo-Based Rainwater Collection Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10The Roo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Gutters and Downspouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10First-Flush Diverters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Untreated-Water Storage Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Sizing the Collection and Storage Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Step 1. Determine Your Annual Water Demand. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Step 2. Determine the Amount o Rainall You Can Capture . . . . . . . . . . . . . . . . . . . . . . . 14Step 3. Determine How Big Your Storage Tank Needs to Be . . . . . . . . . . . . . . . . . . . . . . . 15

Supplemental Sources o Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Sizing Your Water Conveyances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Operation and Maintenance o Your Rainwater Collection System . . . . . . . . . . . . . . . . . . 17

CHAPTER 3. TREATMENT UNITS, PUMPS, AND TREATED-WATER STORAGE . . . 19

Point-o-Entry vs. Point-o-Use Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Treating or Microbiological Contaminants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Filtration Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Disinection Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23


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Ultraviolet Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Chlorine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Other Treatment Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Corrosion Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28VOC/SOC Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Point-o-Use Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Treated-Water Storage Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Supplemental Sources o Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Water Pumps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Sizing the Treatment and Treated-Water Storage Facilities . . . . . . . . . . . . . . . . . . . . . . . . . 34Step 1. Determining Your Maximum (Instantaneous) Consumption Rate . . . . . . . . . . . . . 34Step 2. Designing Your Treated-Water Supply Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Operation and Maintenance o Your Rainwater Treatment System . . . . . . . . . . . . . . . . . . . 36

CHAPTER 4. NONPOTABLE USE AND OTHER CONSIDERATIONS . . . . . . . . . . . . . 37

Nonpotable Harvesting, Storage, and Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Dual Distribution Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Cross-connection Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Piping Labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Air Gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Reduced-Pressure Principle Backfow Assemblies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40Public Water System Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

APPENDIXES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Appendix 1. Rainwater Collection and Untreated Water Storage . . . . . . . . . . . . . . . . . . . . 41

Appendix 2. Treatment System without a Treated-Water Storage Tank . . . . . . . . . . . . . . . . 42

Appendix 3. Treatment System with a Treated-Water Storage Tank . . . . . . . . . . . . . . . . . . 43

TABLES

1.1. Types and Sources o Pathogens That Can Be Found in Harvested Rainwater . . . . . . . . . . . 5

2.1. Amount o Liquid Bleach Needed to Disinect a Storage Tank . . . . . . . . . . . . . . . . . . . . . . 173.1. Microbiological Removal/Inactivation Requirements or Public Water Systems . . . . . . . . . 21

3.2. Filter Technologies and the Type o Microbes They Can Remove . . . . . . . . . . . . . . . . . . . . 22

3.3. UV Dose Requirements or Cryptosporidium, Giardia, and Virus Inactivation . . . . . . . . . . 24

3.4. An Example o Chlorine Contact Time Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.5. An Example o the Eect o pH, Temperature, and Chlorine Concentration . . . . . . . . . . . 26

4.1. Comparison o Nonpotable and Potable Rainwater Systems . . . . . . . . . . . . . . . . . . . . . . . . 38


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Preface

This publication oers guidance or individuals who want to install a rainwater harvestingand treatment system to supply potable drinking water or a single household. It isdesigned to augment the inormation contained in two publications rom the Texas WaterDevelopment Board (TWDB): The Texas Manual on Rainwater Harvestingand RainwaterHarvesting Potential and Guidelines for Texas.

Terms Used in This GuideIn this document, the term potable water reers to water that is used or drinking, oodpreparation, hand washing, dish washing, bathing, or any other purpose that could possiblyresult in the ingestion o the water or its touching the skin. It does not include water that isused only or watering the lawn, washing clothes, or fushing toilets.

We or our, as used in this guide, reer to the Texas Commission on EnvironmentalQuality (TCEQ)specically, the Public Drinking Water Section o the Water SupplyDivision. And you reers to the person or entity that is developing or using a rainwatercollection and treatment system.

There are also numerous reerences to various ANSI/NSF standards and NSF protocolsthroughout this guidance. When we reer to an ANSI/NSF standard, we are identiying aspecic standard that was developed jointly by the American National Standards Institute(ANSI) and the National Sanitation Foundation (NSF). When we mention NSF protocols,we are reerring to a testing protocol used by the National Sanitation Foundation.

This inormational guidance document does not apply to systems

that will serve 15 or more connections (such as homes, apartments, or

businesses) or to those that serve 25 people or more or at least 60 days

each year. These large systems are regulated by various state and ederal

agencies and must meet special requirements that apply to public water

systems. For inormation about the requirements that apply to public

water systems, contact the TCEQs public drinking water program,

at 512-239-4691.


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Other Guidance DocumentsThere are a number o other guidance documents that you may nd helpul when developingyour rainwater harvesting and treatment system. These publications include:

The Texas Manual on Rainwater Harvesting.This document is published by the Texas Water Development Board. A copy can bedownloaded rom the web page .We will reer to it here as the TWDB Manual.

Rainwater Harvesting Potential and Guidelines for Texas.This document was developed in 2006 by the Texas Rainwater Harvesting EvaluationCommittee and is published by the Texas Water Development Board. You can downloada copy rom the same web page, (clickon RWHEC Drat Report). We will reer to it here as the Committee Report.

Guidelines on Rainwater Catchment Systems for Hawaii.This document is published by the College o Tropical Agriculture and HumanResources at the University o Hawaii at Manoa. You can download a copy o thisdocument rom the web page .We will requently reer to it here as the Hawaii Guidelines.
http://www.twdb.state.tx.us/iwt/rainwater/docs.htmlhttp://www.twdb.state.tx.us/iwt/rainwater/docs.htmlhttp://www.ctahr.hawaii.edu/oc/freepubs/pdf/RM-12.pdfhttp://www.ctahr.hawaii.edu/oc/freepubs/pdf/RM-12.pdfhttp://www.twdb.state.tx.us/iwt/rainwater/docs.htmlhttp://www.twdb.state.tx.us/iwt/rainwater/docs.html


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air gap. The atmospheric space betweenthe outlet o a pipe that lls a tank and the

maximum water level in the tank. The verticaldistance between the pipe outlet and the watermust be large enough to prevent water rombacking up into the pipe.

ANSI. American National Standards Institute

contaminant. Any chemical, microbe, orother material that is not ound in pure waterand that can make water unsuitable or itsintended use. Some contaminants only aect

aesthetic qualities such as the appearance,taste, or odor o the water, while others canproduce adverse health eects i present inhigh concentrations.

debris.A contaminant that you can see.Debris can include leaves and twigs, dust anddirt, bird and animal droppings, and insects.

drinking water. See potable water. (Inthis document, the terms drinking water,

potable water, and treated water are usedinterchangeably.)

erosion chlorinator.An in-line treatmentunit that contains calcium hypochlorite tabletsor pellets. As water fows through an erosionchlorinator, the calcium hypochlorite slowlydissolves and releases chlorine into the water.

log removal/inactivation.A unit omeasurement that expresses the percent o

organisms removed or inactivated in termso powers o 10, or logs. For example, a99% reduction in the number o organisms isequivalent to a 2-log reduction, because only1/100th (or 1/102) o the original number willremain ater treatment.

mg/L (milligrams per liter).A unit omeasurement; the amount o a chemical

ound in each liter o water.

mJ/cm2 (millijoules per square centimeter).A unit o measurement; the amount oultraviolet light energy applied to each squarecentimeter o a surace.

NSF. National Sanitation Foundation

nonpathogenic microbe.A bacteria, parasite,or virus that does not cause an inection or

disease in humans.

nonpotable water.Water that may havereceived some treatment but not enough tomake it sae or potable use. Nonpotable watercan be used or watering lawns and gardens,washing clothes, or fushing toilets, but shouldnot be used or any purpose that might resultin the ingestion o the water or its contactwith the skin.

pathogenic microbe.A bacteria, parasite, andvirus that can cause an inection or disease inhumans.

potable water. Water that is used orpreparing ood or beverages or humanconsumption, or washing dishes and utensilsthat are used to prepare or consume oodor beverages, or bathing, or or any otherpurpose that might result in the ingestion owater or its contact with the skin. It does not

include water that is used only or landscapeirrigation, washing clothes, or fushing toilets.(In this document, the terms potable water,drinking water, and treated water, are usedinterchangeably.)

Glossary

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point o entry. The point where water entersa homes plumbing system. A point-o-entry

treatment unit treats all o the water enteringthe home rather than treating the water at thepoint where it is consumed. A whole-housewater sotener is an example o a commonpoint-o-entry treatment unit.

point o use.A point in a home where wateris actually used. A carbon lter installed underthe sink is an example o a common point-o-use treatment unit.

public water system.A public water system(PWS) is any system that serves at least 25people per day or at least 60 days each year orthat serves at least 15 service connections suchas homes, apartments, or businesses.

psi (pounds per square inch).A unit omeasure; the amount o pressure applied toeach square inch o a surace.

SOC (synthetic organic chemical). A typeo organic molecule that is typically ound in

pesticides, herbicides, and similar man-madeproducts.

treated water.Water that has been lteredand disinected and is sae or potable use.In this guidance, the terms treated water,drinking water, and potable water are usedinterchangeably.

untreated water.Water that has not receivedenough treatment to make it sae or

potable use.

VOC (volatile organic chemical).A typeo organic molecule that is typically oundin rened organic products such as plastics,glues, and solvents, as well as gasoline, greases,and oils.

Glossary (continued)


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Chapter 1

Introduction

Rainwater and snowmelt are the primary sources o all drinking water on theplanet. Rainwater harvesting is the practice o collecting the water producedduring rainall events beore it has a chance to run o into a river or stream orsoak into the ground and become groundwater. Rainwater harvesting can beclassied into two broad categories: land-based and roo-based. Land-basedrainwater harvesting occurs when rainwater runo rom the land is collected inponds and small impoundments beore it has a chance to reach a river or stream.Roo-based harvesting, on the other hand, involves collecting the rainwater thatalls on a roo beore the water even reaches the ground.

Although roo-based systems generally produce water with lower levels o chemical and biological

contaminants, the water produced by both systems is subject to contamination and must be properlytreated beore it can be used. The level o treatment you need to provide depends, to a great extent,on whether you will be using the water or potable purposes (such as drinking, ood preparation,bathing, and dish- or hand-washing) or or nonpotable purposes (such as toilet fushing, clotheswashing, and watering). Obviously, rainwater that is intended or potable purposes must receive ahigher level o treatment than rainwater that is intended or irrigation purposes.

From a regulatory perspective, the Texas Commission on Environmental Quality (TCEQ) has rulesthat only apply to a rainwater system that supplies potable water or a public water system1 or orany business that manuactures ood or beverages. We do not set minimum treatment requirementsor rainwater that will be used as a drinking water source or a single household nor do we regulate

nonpotable uses o rainwater.

I you have access to a public water system, we encourage you to utilize your rainwatercollection system or nonpotable use only. This approach will:

Reduce your construction, treatment, and operational costs, because lesstreatment is required or nonpotable uses than or potable uses.

Lower your monthly water bill because you will need to buy less o the publicwater systems drinking water or nonpotable use.

Conserve the natural resources being developed and utilized by your publicwater system.

Chapter 4 contains inormation about how you can use a rainwater harvesting systemto reduce the amount o water that you purchase rom your public water system.

1. A public water system (PWS) is any system that serves at least 25 people per day or at least 60 days each year or that serves at least 15 serviceconnections such as homes, apartments, or businesses. See 30 TAC 290.38(47) or the complete denition o a PWS.


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Purpose and Organizationo This Document

We created this guidance document to help you design and operate a roo-based rainwater harvestingsystem to supply drinking water or you and your household. It is intended to augment theinormation contained in The Texas Manual on Rainwater Harvestingand the Rainwater HarvestingPotential and Guidelines for Texas, which are published by the Texas Water Development Board(TWDB). Although some o the issues we discuss will help you design other types o rainwaterharvesting systems, this document ocuses on the inormation you need to make sure that yoursystem will produce water that is chemically and biologically sae to drink.

Any domestic rainwater harvesting system you use to produce drinking water or your home willconsist o the ollowing six basic components.

1. Catchment surace: This catches the raindrops as they all rom the sky and then channels the

water to a collection gutter.2. Gutters and downspouts: These channel water rom the roo to the tanks that store

untreated water.

3. Lea screens, rst-fush diverters, and roo washers: These components remove debris and dustrom the captured rainwater beore it goes into the tank.

4. Untreated-water storage tanks, or cisterns: These are receptacles that store the harvestedrainwater until you are ready to treat and use it.

5. Treatment/purication acilities: These are lters and disinection equipment that removecontaminants rom the untreated rainwater and make it sae to drink.

6. Treated water storage and distribution system: This includes storage tanks, service pumps,pressure tanks, and water lines that are used to send water to the point where it is consumed.

Summary of This Guidance Manual

Chapter 1. IntroductionProvides background inormation and explains why it is important to properly design and operateyour rainwater harvesting system.

Chapter 2. Collection and Storage o Untreated RainwaterCovers the rst our rainwater system components and describes some o the things that you needto consider when you design your roo-based rainwater collector and the tank where you store your

harvested rainwater beore treating it.Chapter 3. Treatment Units, Pumps, and Treated-Water StorageCovers the last two rainwater system components and discusses the various technologies that you canuse to lter and disinect your rainwater prior to consumption, and covers some o the actors thatwill infuence your design.

Chapter 4. Nonpotable Uses and Other ConsiderationsDiscusses some o the issues you need to consider when designing a rainwater harvesting system toproduce nonpotable water or indoor or outdoor use.


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What Kinds o ContaminantsCan Be Found in Rainwater?

Rainwater and snowall are the ultimate sources o all drinking water on the planet. Rainwater andmelted snow runs o the land and collects in lakes and rivers. They also seep through the groundand recharge the aquiers that supply drinking water wells. Regardless o where you currently obtainyour drinking water, it originally ell rom the sky.

The water in a raindrop is one o the cleanest sources o water available. Rainwater can absorb gasessuch as carbon dioxide, oxygen, nitrogen dioxide, and sulur dioxide rom the atmosphere. It can alsocapture soot and other microscopic particulates as it alls through the sky. Nevertheless, rainwater isalmost 100% pure water beore it reaches the ground.

Pure water is considered the universal solvent; it can absorb or dissolve contaminants rom almostanything it comes into contact with. That is why it is especially important to design and operate your

system so that the rainwater picks up as ew contaminants as possible beore you consume it.

Debris

We use the term debris to describe any contaminant that you can see. Debris includes leaves andtwigs, dust and dirt, bird and animal droppings, insects, and other visible material. Although debrisobviously reduces the aesthetic quality o the water, it can also pose unseen chemical and biologicalhealth threats. For example, leaves and dust can contain unseen chemical contaminants such asherbicides and pesticides. Similarly, bird and animal droppings can contain microscopic parasites,bacteria, and viruses.

Chemical Contaminants

Although rainwater can be contaminated by absorbing airborne chemicals, most o the chemicalspresent in harvested rainwater are introduced during collection, treatment, and distribution. Byproperly designing and operating your rainwater harvesting system, you can minimize your exposureto a variety o chemical contaminants that include organic chemicals, such as volatile and syntheticorganics, and inorganic chemicals, such as minerals and metals.

Volatile Organic Chemicals

Volatile organic chemicals (VOCs) can be introduced when rainwater comes into contact with

materials containing rened organic products. These VOC sources include plastics, glues, andsolvents, as well as gasoline, greases, and oils. Most VOC contamination at rainwater systemsoccurs because the materials used to construct the system were not manuactured specicallyor drinking water applications; these materials may not meet the standards set or potablewater products and may release undesirable levels o VOCs into the water. Although most VOCcontamination results rom improper construction practices, VOC contamination can also occurwhen raindrops all through an atmosphere containing gasoline or solvent vapors.


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Synthetic Organic Chemicals

Synthetic organic chemicals (SOCs) are chemicals that are typically ound in pesticides,herbicides, and similar man-made products. Since SOCs are not very volatile, these contaminantsare usually introduced when debris such as dust and leaves are allowed to enter the system.However, SOC contamination can also be introduced i you install your rainwater collection

and storage system in an area where aerial herbicide or pesticide application occurs. Regardlesso how the chemical reaches the rainwater system, SOC contamination is usually the result oenvironmental exposure rather than poor construction practices.

MineralsMinerals are inorganic materials ound naturally in the environment. Most minerals areinorganic salts (such as calcium carbonate, sodium bicarbonate, magnesium sulate, and sodiumchloride) that aect the favor o the water but generally do not pose an actual health threat. Themost signicant exception to this general rule o thumb is asbestos, which is a amily o broussilica salts used to manuacture a variety o products. Under certain conditions, some o theseproducts can release a orm o asbestos that can pose a long-term health threat i ingested

or inhaled.

Minerals, especially calcium and magnesium salts, are what gives water its hardness. Rainwatercontains virtually no minerals beore it is harvested and so it is a very sot water. It is also slightlyacidic, with a pH around 5.6, due to the carbon, nitrogen, and sulur dioxides it absorbs romthe atmosphere. Because it takes time or rainwater to absorb minerals, most o the mineralspresent in harvested rainwater will have been leached rom materials used to construct the systemrather than rom environmental sources.

Metals

Metals include lead, arsenic, copper, iron, and manganese. Some metals, such as lead and arsenic,

can pose a long-term health threat i they are present in high enough concentrations. Othermetals, such as iron and manganese, can aect the appearance and taste o the water but pose nohealth threat. It takes time or metal to dissolve in rainwater. Thereore, this type o contaminantis usually present only ater metallic materials such as lead solder, iron and copper pipe, and brassttings have been exposed to rainwater or several hours or longer.

Microbiological Contaminants

Rainwater seldom contains any type o microbiological contaminant until it is harvested and stored.The water in a raindrop is extremely pure, but it is virtually impossible to maintain that level opurity during the collection, treatment, and distribution processes. Rainwater can be contaminatedby two major categories o microbiological agents: those that cause disease and those that do not.Microbiological contaminants that can cause a disease or inection are called pathogenic, while thosethat do not are called nonpathogenic.

Nonpathogenic organisms can be present in high numbers regardless o where your home is located.These nonpathogenic microbes include many kinds o protozoa, algae, bacteria, and viruses.Although they do not cause illness, nonpathogens oten reduce the aesthetic quality o the waterand can interere with the operation o the rainwater harvesting and treatment acilities, increasing


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operational and maintenance requirements. For example, high concentrations o algae can makethe water slimy, plugging the lters used to treat the water, or ungi and bacteria can colonize in thewater lines in your home.

Pathogenic organisms are not normally ound in rainwater. However, they can be present i therainwater collection or storage acilities have been contaminated by ecal material such as animal

or bird droppings. Pathogenic microbes pose a greater health threat to rainwater users than mostchemical contaminants, or a number o reasons, including:

Pathogens can cause disease ater a single exposure, while most chemical contaminants mayrequire months or even years o exposure beore causing a health eect.

Pathogens do not aect the taste, smell, or appearance o the water. Many chemicalcontaminants, on the other hand, make the water taste, smell, or look dierent, especially i thechemicals are present at levels that would pose a short-term risk.

Pathogen levels can rise very quickly, while chemical levels tend to remain airly constant.Consequently, it is relatively easy (though somewhat costly) to periodically test or chemical

contaminants, while it is both dicult and costly to continuously test or most pathogens. A disease caused by pathogens can usually be passed rom person to person, while the health

eects caused by chemicals aect only those that actually consume the contaminated water.

Waterborne illnesses caused by pathogens can be a serious health risk or the elderly, inants,chemotherapy patients, and other individuals with a delicate or weakened immune system.

Pathogenic microbiological contaminants include certain types o protozoan parasites, bacteria, andviruses. The inectivity rates (the number o microbes required to cause a disease) and the virulence(the severity o the disease) vary, depending on the type o pathogen present and the immune systemo the person that is exposed. Some pathogens can cause an illness i a person with a weakenedimmune system is exposed to just a ew organisms.

Some o the pathogens that can be introduced through improperly designed and operated rainwatersystems are shown in Table 1.1.

Type o Pathogen Organism Source

Parasite

Giardia lamblia cats and wild animals

Cryptosporidium parvum cats, birds, rodents, and reptiles

Toxoplasma gondii cats, birds, and rodents

Bacteria

Campylobacter spp. birds and rats

Salmonella spp . cats, birds, rodents, and reptiles

Leptospira spp. mammals

Escherichia coli birds and mammals

Virus Hantavirus spp. rodents

Table 1.1. Types and Sources o Pathogens That Can Be Found in Harvested Rainwater


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Product Certications

To ensure that your rainwater system will provide you with sae drinking water, the AmericanNational Standards Institute (ANSI) has coordinated the development o various standards or

products that are used to construct rainwater harvesting systems or potable water. To identiyproducts that meet these standards, ANSI also accredits organizations that conduct certicationtests. You can nd out more about the ANSI organization and its accreditation program on

the ANSI web site.

American National Standards Institutewww.ansi.org

The ANSI web site also provides a list o accredited testers and the types o products they certiy,as well as links to their respective web sites. The address or this web page is:.

Whenever possible, you should use products that have been independently tested and certiedin accordance with nationally-recognized standards. Although there are other accredited testingorganizations, the two that we are most amiliar with are the National Sanitation Foundation (NSF)and Underwriters Laboratories (UL). You can obtain a list o all o the drinking water products thatthey have certied by checking their respective web sites.

National Sanitation Foundationhttp://ns.org/consumer/drinking_water

Underwriters Laboratories, Inc.

www.ul.com/water/prodcert/waterqry.html

Products that have been tested and certied in accordance with ANSI/NSF standards will bear theseal o the organization that tested the product, and usually identiy the standard or protocol thatwas used. Some examples o the seals are shown below.

Although we will ocus on the health-related standards, you also need to consider other UL saetystandards that apply when you select pumps, switches, and other electrical components.

IN ACCORDANCE WITH

ANSI/NSF 61

WATER QUALITY

NSF/ANSI 55 CLASS A CERTIFIED

Certifed to

NSF/ANSI 60
http://www.ansi.org/http://www.ansi.org/conformity_assessment/accreditation_programs/product_certifiers.aspxhttp://nsf.org/consumer/drinking_waterhttp://www.ul.com/water/prodcert/waterqry.htmlhttp://www.ul.com/water/prodcert/waterqry.htmlhttp://nsf.org/consumer/drinking_waterhttp://www.ansi.org/conformity_assessment/accreditation_programs/product_certifiers.aspxhttp://www.ansi.org/


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Chapter 2

Collection and Storage of

Untreated Rainwater

As you plan your rainwater collection and storage acilities, you need tokeep two things in mind.

1. The catchment and storage acilities must be designed so that they reducepotential sources o contamination.

2. The catchment surace and storage tanks must be large enough to captureand store enough rainwater to last you until the next time it rains.Otherwise, you will need to identiy a supplemental source o water.

This chapter provides you with the basic inormation that you need to achievethese two objectives.


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0

Roo-Based Rainwater Collection Systems

As we mentioned in Chapter 1, rainwater collection systems or potable water can be land-based orroo-based. Land-based collectors, however, are much more susceptible to chemical and biological

contamination than roo-based systems. Thereore, you should not use a land-based system toprovide untreated water or a potable water system, unless you are willing to design and operate asophisticated treatment system and routinely monitor the chemical and microbiological quality oyour treated water. It is preerable to use a roo-based collection system. A simple schematic o a roo-based rainwater collection system is shown at the end o this document (Appendix 1).

The Roof

The roo you use to collect the rainwater can be constructed using a variety o materials. Chapter2 in the TWDB Manual and Section 1 in the Hawaii Guidelines contain good discussions oyour options. We recommend that you use a smooth, nonporous material because it improves

the eciency o your system by absorbing less water and reducing the chance that microbes anddebris will collect in the pores and seams o the roo. Although we dont know o any roongmaterial that has been designed specically or potable water catchment, you should probably avoidusing composite, asphalt, or asbestos shingles when you construct your roo. It is also extremelyimportant that you NOT use any roong material that contains ungicides, algaecides, or any otherbiocide compound. As these products age and decay, they release a variety o organic and inorganicchemicals that can pose a health threat i consumed. Although there are some treatment technologycombinations, such as activated carbon lters ollowed by reverse osmosis, that can remove thesecontaminants, you should not risk exposing yoursel and your amily to these health threats.

I possible, your roo should have a steep slope. During the periods between rainall events, dust and

debris can accumulate on the roo. It is much easier to rinse the debris rom a well-pitched roo thanit is rom a roo that is level or that only has a slight incline. As the TWDB Manual indicates, it alsotakes a much heavier rainall event to rinse a level roo than an inclined one.

I you are going to coat your roo with a sealant or paint, we recommend that you use one thathas been certied under NSF Protocol P151 or ANSI/NSF Standard 61. NSF Protocol P151 wasdeveloped specically or testing rainwater harvesting and collection systems while ANSI/NSFStandard 61 is a more general standard that applies to all materials that come into contact withpotable water. Products certied under either o these requirements are approved or potable waterapplications and are unlikely to contaminate your water i properly applied. As we discussed inChapter 1, materials that have been certied in accordance with ANSI/NSF requirements bear the

label o the organization that tested the product.

Gutters and Downspouts

Gutters, downspouts, and piping are used to collect the water harvested rom your roo and conveyit to the tanks that will store it prior to treatment. Chapter 2 in the TWDB Manual and Section 1in the Hawaii Guidelines contain several illustrations that will help you design a sae and eectiveconveyance system.


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We recommend that you install a seamless aluminum gutter or construct your gutter using a plasticpipe that meets the requirements o ANSI/NSF Standard 14 or Standard 61. We do not know o anyaluminum gutter that has been certied under either NSF Protocol P151 or ANSI/NSF Standard61. However, aluminum is a relatively inert material that oxidizes very slowly. Seamless aluminum,thereore, should be relatively sae to use and allows you to avoid joint seams, which can harbor

bacteria and algal growths. PVC pipe that meets ANSI/NSF requirements is readily available and willbear an ANSI/NSF label along the length o the pipe. However, PVC gutters will probably not lastas long as seamless aluminum gutters, because plastics are more vulnerable to sunlight damage anddecay than aluminum.

You will need to consider several other actors as you design your gutters, downspouts, and piping.

Your gutter should gradually (but continuously) slope toward the downspout. I you do notproperly slope the gutter, it will not drain completely and algae and bacteria will begin to growin the water that remains ater the rainall event. For best eciency, the gutter should haveabout a 1% slope (in other words, the bottom o the gutter should drop 1 inch or every 8 eeto gutter length).

I your roo tends to capture leaves, twigs, or other large debris, you should install a lea guard,gutter screen, or other similar material on the top o your gutter. The lea guard that you selectshould be sel-cleaningthat is, it should fush the debris away rom the gutter rather thantrapping the material directly above it. I you do not have much trouble with leaves and twigs,you will probably nd that a basket screen or unnel screen located at each gullet downspoutprovides adequate protection without obstructing water fow. Although we know o no leaguard or screen that has been certied under Protocol P151 or Standard 61, it is probablybetter to prevent large debris rom entering the system than to avoid the use o unapprovedmaterials.

Your conveyance system should prevent water rom pooling at any point between the roo and

your untreated-water storage tank. I you cannot design the piping system so that it drainscompletely between rainall events, you must incorporate additional equipment to ensure thatstagnant water is fushed rom the piping beore it enters the storage tank.

First-Flush Diverters

As discussed previously, roo-based collectors are much less susceptible to chemical and biologicalcontamination than land-based collectors. Nevertheless, even well-designed roos will collect somecontaminants during the periods between rainall events. Although a lea guard or gutter screen cankeep large debris out o your system, you will need to use a rst-fush diverter to keep most o thedust, dirt, chemical contaminants, or animal and bird droppings out o the untreated-water storage

tank. Most o these contaminants will be rinsed o the roo during the rst ew minutes o a majorrainall event. In order to prevent them rom reaching your storage tank, you need to install a rst-fush diverter on each downspout that discharges to the tank.

As Chapter 2 in the TWDB Manual indicates, the amount o water needed to rinse the roo dependson a number o actors, including:

Slope o the roo. Steeply inclined roos will rinse more quickly than roos that only have aslight incline.


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Porosity o the roong material. Nonporous materials (such as metal) will clean more quicklythan porous materials.

Amount and type o contaminant present. Although the concentration o all contaminantstend to increase as time passes between rainall events, dust and small debris are much easier toremove than ecal matter.

Rainall rate. Long, slow drizzles will fush ewer contaminants than brie heavy rainall.

There are two types o rst-fush diverters. One type diverts a xed volume o water beore the tankbegins to ll and the other begins lling the tank only ater the rainall rate reaches a certain level.Experts have not reached a consensus on which type o diverter is better. You may want to considerthe ollowing two issues when selecting the type and size o diverter you will use.

Rainall events typically begin with a slow drizzle and then increase in intensity. I you use axed volume diverter, you may not be able to completely fush contaminants rom the roobeore the diverter is lled and water begins fowing to the untreated-water storage tank.

I rainall intensity doesnt increase signicantly over the course o the rainall event, some

contaminants may remain on the roo. In this case, a xed rate diverter may waste a lot owater that doesnt contain many contaminants.

Chapter 2 o the TWDB Manual describes a couple o rst-fush diverters and discusses the actorsthat can infuence their perormance. I you use a xed volume diverter, we recommend that yousize it so that it will fush at least 1 to 2 gallons o water or every 100 square eet o roo surace. Forexample, i your roo is 30 eet wide and 80 eet long, you would want to size your device to divertabout 25 to 50 gallons o water.

100 square eet will divert 1 to 2 gallons o water

30 eet 80 eet = 2,400 square eet (total roo area)

2,400 square eet 100 square eet = 24 units o 100 square eet

24 1 to 2 gallons = 24 to 48 gallons

Piping

We recommend that you use a plastic pipe that has been certied to meet ANSI/NSF Standard 14 orStandard 61 requirements. Although other piping materials are available, plastics are probably yourbest choice. Rainwater is very sot and somewhat acidic, so it tends to be more corrosive that mostother sources o drinking water. Since plastic pipe is less susceptible to corrosion, it is more suitableor this application. However, as noted previously, plastic pipe is more susceptible to UV damagethan metal pipe. You may want to paint the outside o the piping that is exposed to sunlight in order

to protect it rom UV rays. I you decide to use another piping material, be sure that it has beencertied under Standard 14 or Standard 61. Without the ANSI/NSF certication, you have no wayto know whether the pipe has been tested and whether it is acceptable or potable water use. Due tothe corrosive tendencies o rainwater, you should NOT use thin-wall copper pipe or tubing, even i itis ANSI/NSF certied, because o its potential to develop pinhole leaks.


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Untreated-Water Storage Systems

The untreated-rainwater storage acilities will probably be the most costly part o your system. You canuse a variety o materials and types o design in constructing a tank to store your harvested rainwater

prior to treatment. There are several issues that you should consider in constructing your tank.To ensure that your untreated-water storage acilities are structurally sound, these acilities need to bedesigned by individuals that are amiliar with the structural properties o the materials that you selectand the soil characteristics at the installation site. A gallon o water weighs 8.34 pounds, so a tankthat holds 5,000 gallons o water will weigh more than 41,500 pounds when it is ull.

The tank must be structurally sound. Chapter 2 o the TWDB Manual and Section 2 o the HawaiiGuidelines discuss the various materials that have been used to build rainwater storage tanks anddescribe some o the advantages and disadvantages o each material. The materials you select must bestrong enough to withstand any internal pressure generated by the water and any external pressuregenerated by the surrounding environment. We recommend that you hire a licensed proessional

engineer or other experienced proessional to design your storage acilities, especially i you areinstalling a tank below ground level or an above-ground tank with a capacity o 10,000 gallonsor more.

I you install an above-ground storage tank, your contractor will help you design a pad that willassure that the tank remains level as the soil shrinks and swells. I you install a subsurace tank, yourcontractor will make sure that the tank is properly bedded so that it will be protected rom soilmovement, is constructed o material that is very corrosion-resistant, and is not installed in an areawith a high water table. You should not install your tank below the water table because it can shit oreven foat when it is empty.

We suggest that you use an above ground tank i possible because they are more accessible and can

be easily inspected, cleaned, and repaired. However, above ground tanks are usually more susceptibleto impact damage and may need to be enced or otherwise protected. Also, remember that aboveground tanks are exposed to sunlight and need to be protected rom UV degradation, especially iyou use plastic or other UV-sensitive materials.

All the openings in your tank need to be sealed, screened, or covered, in order to prevent insects,lizards, birds, and rodents rom getting into your tank. You should seal all unnecessary openings witha bolted, gasketed cover. You must also make sure that the open end o all vents and overfows acedownward and are covered with a corrosion-resistant window-screen material. In order to preventfies and mosquitoes rom using your tank as a breeding ground, there must be no gap larger than1/16th o an inch at any opening into the tank. Painting the inside o the vents black may also help

because insects will perceive the opening as a solid surace. Since the gutter and downspout are opento the atmosphere, you should probably install an insect screen or a prelter (such as the one shownin Figure 2-4 o the TWDB Manual) at the inlet to the storage tank.

The suraces that come into direct contact with the water must be nonporous and suitable orpotable water applications. I you construct the tank out o materials that have not been certied inaccordance with NSF Protocol P151 or ANSI/NSF Standard 61, you will need to coat the insidesuraces with a certied coating material or use a certied liner or bladder.


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Sizing the Collection and Storage Facilities

The proper sizes or your catchment surace and your water storage tank depends on how oten andhow hard it rains at your home, as well as on how much water you and your amily use. Chapter 4

in the TWDB Manual explains how this inormation is used to calculate the sizes o your collectionand storage acilities.

Step 1. Determine Your Annual Water Demand

The rst thing that you need to do is to gure out how much potable water you and your amilyneed each day. Your water demand depends on how many people are in your household and whatyou use the water or. As a general rule, we recommend that you design your system so that it canprovide at least 50 gallons o water per day or each person in your amily.

However, your amily may need more or less water, depending upon your water-use patterns andthe type o plumbing xtures you have. For example, you do not need to provide water or doing

laundry i your amily takes its clothes to a laundromat rather than washing them at home. On theother hand, you may use more water than average i your amily likes to take baths instead o shortshowers with a water-conserving shower head. Chapter 4 in the TWDB Manual provides a handytable that you can use to estimate your actual daily water needs. Once you determine your dailywater needs, you can determine your annual demand, by multiplying your daily water needs by 365.Heres an example o this calculation or a amily o our:

4 people 50 gallons = 200 gallons o water used per day

200 gallons 365 days = 73,000 gallons o water used per year

Step 2. Determine the Amount o Rainall You Can Capture

As discussed previously, the shape o the roo and the material you use to construct it do aect theeciency o your system. However, the actor that has the greatest impact is the amount o area thatis covered by the roo, or its ootprint. Unless your roo and gutter system is extremely ecient, eachinch o rain will produce approximately12 gallon o water or every square oot o area covered bythe roo. Figure 4-2 in the TWDB Manual is a map showing the average rainall across Texas. Todetermine the amount o water you will capture, you need to multiply the annual inches o rainallyou get at your home by 0.5, which will give you the annual number o gallons o water you willcollect per square oot o collection area. Then multiply that number by the square ootage o thearea cover by your roo (ootprint). For example, i your ootprint is 2,500 square eet, and yourannual rainall is 40 inches:

40 inches (o rain per year) 0.5 gallons (per inch o rain) = 20 gallons (per square oot)20 gallons 2,500 square eet = 50,000 gallons per year

In this example, the ootprint o your roo and the location o your home will not allow you tocollect enough water to meet all the water needs o your amily o our, even on an average year. Nowyou have two choices; you must either reduce your annual use, or you must increase your supply. Youcan increase your supply in one o two ways; you can supplement your rainwater supply with waterrom another source (such as potable water supplied by a water hauler or public water system) or youcan increase the size o your collection system so that it can capture enough water.


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Step 3. Determine How Big Your Storage Tank Needs to Be

Your untreated-water storage tank must be able to store enough water to meet or exceed the amounto water your household will use during periods o little or no rainall. Figure 4-3 in the TWDBManual shows the maximum number o continuous dry days that you can expect to have based onwhere you live. To determine how much storage you need, you must multiply your daily use by the

number o continuous dry days you can expect in one year. For example,

4 people 50 gallons = 200 gallons per day

200 gallons 50 dry days = 10,000 gallons

You might be able to get by with a smaller untreated-water storage tank i you are going to use asupplemental drinking water supply to meet part o your amilys needs.

Supplemental Sources of Supply

I you are going to connect your tank to a supply line rom a public water system, the connection

must be made through an air gap and must be inspected and approved by the public watersystems personnel.

I you are going to obtain a supplemental supply rom a water hauler, you need to make sure that:

Your tank is equipped with a roo hatch or has a covered ll box.

The tanker truck and hoses that the supplier uses are only used to transport potable water.

The supplier obtains your water rom a public water system.

The ends o the ll line and hoses are capped or otherwise protected rom contaminationduring transport.

The supplier does not drop the end o the hose into the tank (because the outside o the hose is

oten much less sanitary than the inside o the hose). The supplier closes the hatch or ll box when they nish lling your tank.


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Sizing Your Water Conveyances

Gutters, downspouts, rst-fush diverters, and piping are used to transport, or convey, water rom theroo to your untreated-water storage tank. To maximize the eciency o your rainwater harvesting

system, you have to design these conveyances so that they can handle all o the water that is capturedon the roo during each rainall. The size o these components depends on a number o actors,including the maximum rainall rate, the ootprint and shape o the roo, and the number o pointswhere water is diverted to the storage tank. Chapter 2 o the TWDB Manual discusses many o theissues you will need to consider.

In most cases, a 4-inch gutter and piping system will be adequate to meet your needs. However, youshould consider gutters and piping that are 6 inches or larger i your roo has a large ootprint ornumerous ridges and valleys, or i there is more than 80 eet or so to the nearest downspout. The bestthing to do when sizing your conveyances is to consult with a reputable gutter supplier.


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Operation and Maintenance oYour Rainwater Collection System

Rainwater collection and storage acilities require a variety o routine maintenance. Some o theroutine maintenance activities that you will need to periodically complete are:

Removing debris rom the roo, lea guard, gutter, gutter screen, and rst-fush diverter.

Inspecting and repairing vent screens.

Siphoning sediment rom the tank.

Testing the coliorm bacteria levels in your untreated-water storage tank.

Disinecting the untreated-water storage tank i total coliorm levels reach 500 colony-ormingunits per 100 milliliters (500 CFU/100 mL) or i ecal coliorm levels reach 100 CFU/100 mL.

Untreated water with total coliorm levels above 500 CFU/100 mL or ecal coliorm levels rise above

100 CFU/100 mL should not even be used or nonpotable purposes until it has been disinected.Disinection can also help prevent heavy biological growths that can oul your treatment system andcontaminate your plumbing system. The most convenient way or you to control biological growthsin your storage tank is to add a small amount o chlorine bleach periodically. The amount o bleachyou will need to add depends on how concentrated the bleach is, how big the storage tank is, andwhether you are trying to prevent biological growths or eliminate an existing problem. Table 2.1 liststhe amount o bleach needed to achieve chlorine levels under varying conditions.

You should only use chlorine compounds that are certied in accordance with ANSI/NSF Standard60 requirements. This standard, which also applies to all chemicals added to potable water, assuresthat the product will not pose any chemical or biological threat to you or your amily when appliedin accordance with manuacturer recommendations. Unortunately, ew i any o the liquid bleaches

Desired

Chlorine Level

Bleach Concentration

(per bottle label)

Storage Tank

Volume

Approximate Amount

o Bleach Needed

0.5 mg/L

(prevention)

5 %1,000 gal 2 12 Tablespoons

5,000 gal 34 cup

10 %1,000 gal 1 12 Tablespoons

5,000 gal 13 cup

5 mg/L

(elimination)

5 %1,000 gal 1 12 cups

5,000 gal 7 34 cups

10 % 1,000 gal 1

1

2

cups5,000 gal 3 34 cups

Table 2.1. Amount o Liquid Bleach Needed to Disinect a Storage Tank


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sold in grocery stores or pool-supply companies carry an NSF label. Although you can nd a list oapproved liquid bleaches on the NSF web site, most o these manuacturers do not produce smallcontainers o bleach. We try to maintain a list o unlabeled bleaches that meet NSF requirements.We post this list on our web site, at .

I you cannot nd any o the bleach solutions rom our list or the NSFs list, at least avoid the ones

that contain ragrances or UV stabilizers: none o these bleaches are NSF certied. And do not useproducts designed or use in swimming pools. These products oten contain cyanide-basedUV stabilizers.
http://www.tceq.state.tx.us/goto/bleachhttp://www.tceq.state.tx.us/goto/bleach


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Chapter 3

Treatment Units, Pumps,

and Treated-Water Storage

As you design your rainwater treatment and treated-water storage acilities, youneed to keep a ew things in mind.

1. The harvested water must be treated beore it reaches the points in yourhome where it is consumed.

2. The treatment system must be able to protect you and your amily rom avariety o chemical and microbiological contaminants.

3. The treated-water storage tanks must prevent the treated water rombeing recontaminated.

4. The treatment and storage acilities must supply enough water to meetyour amilys needs at the instant that they need it.

This chapter provides you with the basic inormation that you need to achieve these objectives.Simple schematics or treatment, storage, and pumping acilities are shown at the end o thisdocument (Appendixes 2 and 3).


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0

Point-o-Entry vs. Point-o-Use Treatment

Treatment units can be categorized in a variety o ways. For example, some treatment processesare designed to improve the saety o the water, while others are designed to improve its aesthetic

qualities (such as taste and odor). Another way to categorize a treatment unit is by the location inyour home where the treatment occurs. Treatment units that treat all o the water as it enters youhomes plumbing system are called Point-o-Entry, or POE, units while the units that treat thewater at the point where it is actually consumed are called Point-o-Use, or POU, units.

Although the POE and POU approaches can both provide adequate protection i properly installed,we recommend that you install a POE treatment system when treating or contaminants that posea potential health threat. Using a POE system or this application helps to ensure that all the waterentering your home is sae to use, simplies your operational and maintenance requirements, andmay even reduce your installation costs. We recommend that you only use POU systems to improvethe aesthetic quality o your water.


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Treating or Microbiological Contaminants

As we discussed in Chapter 1, harvested rainwater can contain a variety o pathogenic (disease-causing) microbes. Although the water harvested rom a roo-based collection system will usually

contain ew o these microbiological contaminants, you still need to treat the water as though itwere highly contaminated. Providing this level o treatment ensures that your amily is constantlyprotected rom a waterborne disease.

The threat posed by microbiological contaminants is controlled by physically removing thecontaminants with a lter, or by inactivating them with a disinectant. State and ederal regulationsestablish minimum treatment requirements or public water systems that use rainwater systemsand other water sources that are susceptible to microbiological contamination. Although thereare no similar mandatory requirements or individual domestic rainwater harvesting systems, werecommend that you use a treatment system that provides the same level o protection as one thatwould be used by a public water system. Table 3.1 lists the minimum treatment requirements o thecurrent surace water treatment rules or public water systems.

It is dicult to design a single treatment process that provides complete protection against allpathogens. Although it is possible that a ltration system or a disinection system could each achieveadequate levels o protection by themselves, we recommend that you use a combination o ltersand disinectants to provide multiple barriers and increase your protection rom waterborne disease.Regardless o which technology or combination o technologies you select, you should only useequipment that has been certied in accordance with applicable ANSI/NSF requirements. This willensure that your treatment system will oer adequate protection. A properly designed treatment

system will provide you and your amily with a sae, sanitary supply o drinking water. On the otherhand, improperly treated rainwater will, at some point, make you, your amily, or your guestsvery sick.

Filtration Technologies

You can use a variety o technologies to remove microbial pathogens rom your harvested rainwater.Some o these lters can only remove relatively large particles, such as parasites, while other

ContaminantLog

Removal / InactivationEquivalent Percent

Removal / Inactivation

Cryptosporidium 2 99

Giardia 3 99.9

Viruses 4 99.99

Table 3.1. Microbiological Removal/Inactivation Requirements orPublic Water Systems Using Rainwater


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technologies can remove extremely minute particles, such as viruses. Table 3.2 lists some o theltration technologies that you may want to consider and their relative eectiveness or removing themicrobes that could be present in harvested rainwater.

You need to consider several issues when selecting the ltration technology that you want to use.

For example:

The gutter screens and prelters we discussed in Chapter 2 can only remove large particles.They are completely ineective against pathogenic microbes (parasites, bacteria, viruses).

Not all bag and cartridge lters will remove Cryptosporidium and Giardia. You need to select aunit that is specically designed to remove these parasitic pathogens.

Since bag and cartridge lters do not remove bacteria or viruses, you will need to rely entirelyon a disinectant to kill or inactive these pathogens.

Some bag lters can be cleaned and reused, while others must be replaced when they get ull.

Cartridge lters are usually less expensive than bag lters but the cartridges usually cannot becleaned and must be replaced periodically.

Some membrane materials, such as cellulose acetate, are extremely susceptible to damageby chlorine and other disinectants. I you select a unit that uses one o these susceptiblemembranes, you need to install an activated carbon lter upstream o your membrane lterto remove any disinectant that might be present in the water. This activated carbon lter isespecially important i you are going to supplement your rainwater supply with hauled water

or water rom a public water system because we require these water suppliers to maintain adisinectant residual in the water they deliver to you.

Nanoltration and reverse osmosis membranes usually require a higher operating pressure thanmicroltration and ultraltration membranes.

Membrane lters can be plugged by larger-size particles. Thereore, you will probably needto install a cartridge or bag prelter to make sure that large particles do not enter themembrane unit.

Filtration System Types o Pathogens Removed

Some Types o Bag Filters Parasites (Cryptosporidium, Giardia, Toxoplasma)

Some Types o Cartridge Filters Parasites

Microltration Membranes Parasites, most bacteria

Ultraltration Membranes Parasites, bacteria, some viruses

Nanoltration Membranes Parasites, bacteria, viruses

Table 3.2. Filter Technologies and the Type o Microbes They Can Remove


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You must fush and backwash membrane lters periodically to remove the particles thathave been trapped on the membrane surace. Thereore, not all o the water you treat can beconsumed. Depending on the design, the membrane system may only be able to deliver 85 to95% o the water you harvest.

Be sure that you read and ollow the manuacturers instructions. Filtration systems are

usually quite reliable pieces o equipment. However, they can be easily damaged i you dontollow the manuacturers recommendations.

Unless you are going to disinect with a high dose o ultraviolet light, we recommend that youuse lters that have been certied or the removal o parasitic cysts in accordance with ANSI/NSFStandard 53 requirements. Filters that have been certied to meet this requirement have been provensae or drinking water applications and will remove 99.95% oCryptosporidium-size particles. Sincethe other parasites are larger than Cryptosporidium, these lters will protect you and your amily romall o the parasitic pathogens that might be present in harvested rainwater.

Some ltration technologies, especially bag and cartridge lters, are unable to meet the stringentperormance standards established by ANSI/NSF Standard 53. Although some o these units can

reduce Cryptosporidium levels signicantly, you need to make sure that an uncertied unit has beentested in accordance with the United States Environmental Protection Agency (EPA) requirementsby an independent third party. Please eel ree to call us i you are interested in using a bag, cartridge,or membrane lter that has not been certied under ANSI/NSF Standard 53.

I you are going to disinect with a high dose o ultraviolet light, it is not absolutely essential or youto use a lter that is certied to meet ANSI/NSF Standard 53 requirements. However, you must usea lter that removes most particulate matter, because the UV light cannot disinect pathogens thatare shaded by other particles. In order to maximize the eciency o your UV disinection process,we recommend that you install one o the membrane lter technologies or a cartridge lter that hasa pore size o 3 to 5 microns or smaller. In order to assure that the lter does not leach undesirable

contaminants into the water, you should only use ltration systems that that have been certied tomeet ANSI/NSF Standard 61 requirements.

Disinection Technologies

Although there are numerous disinection technologies, some o them are more appropriate orhome use than others. We recommend that you consider using a combination o ultraviolet light andchlorine or the ollowing reasons.

Ultraviolet light (UV) is extremely eective against Cryptosporidium, but high doses arerequired to inactivate some viral pathogens. In addition, UV systems do not maintain adisinectant residual in your plumbing system.

Free chlorine is very eective against viruses but is virtually ineective againstCryptosporidium. In addition, it is easy to maintain and measure a ree chlorineresidual in your plumbing system.

I you do not want to maintain a disinectant residual in your plumbing system, you may wantto consider using ozone as an alternative to UV. Like UV, ozone does not produce a long-lastingresidual and will not provide any protection against bacterial regrowth in your plumbing. However,it is eective against both parasites and viruses. The major reason that we are not recommending


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ozone is that there is no ANSI/NSF standard or evaluating the saety o ozone generators used orpotable water applications. I you do decide to use ozone as your disinectant, be sure to use anozone contact vessel that is certied in accordance with ANSI/NSF Standard 61 requirements.

Ultraviolet Light

As we just discussed, some disinectants are more eective against certain pathogens than others.Ultraviolet light provides an excellent example o this limitation since it is much more eectiveagainst parasites than it is against certain viruses. Table 3.3 shows the UV dose that must be appliedto achieve certain levels o disinection.

As Table 3.3 indicates, the UV dose needed to achieve a 4-log (99.99%) inactivation o virusesis more than eight times greater than the dose needed to achieve an equivalent inactivation oparasites. ANSI/NSF Standard 55 establishes testing requirements or UV water treatment systems.UV systems that meet the Class A requirements o Standard 55 are capable o producing an UVdose o 400 mJ/cm2 at their rated capacity and are equipped with a sensor to alert you i the UVsystem needs to be cleaned or has begun to ail due to lamp age. UV systems that meet the Class

B requirements o Standard 55 are not required to have a sensor and have not been certied orpathogen control, although they can be used to provide additional treatment on water that hasalready been properly disinected. Consequently, i you are going to install a UV system to controlpathogens, you need to choose a unit that is certied as Class A under ANSI/NSF Standard 55.

It is important to remember that UV can only inactivate a pathogen i the microbe has actually beenexposed to the UV light. In order or the UV system to work, the water passing though it must berelatively clear and ree o particles. Consequently, you need to install a lter upstream o your UVunit. (This lter should be one o the lters discussed in the previous section.)

To achieve this levelo Inactivation

This UV dose (mJ/cm2) isrequired or this Pathogen

Log Percent Cryptosporidium Giardia Virus

0.5 67 % 1.6 1.5 39

1.0 90 2.5 2.1 58

1.5 96.7 3.9 3.0 79

2.0 99 5.8 5.2 100

2.5 99.67 8.5 7.7 121

3.0 99.9 12 11 143

3.5 99.97 15 15 163

4.0 99.99 22 22 186

Table 3.3. UV Dose Requirements orCryptosporidium, Giardia, and Virus Inactivation


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Chlorine

Chlorine is one o a group o non-metallic elements know as halogens. Chlorine, like UV, is moreeective against some pathogens than it is against others. However, there are several importantdierences between UV and chlorine, including:

Chlorine is more eective against viruses than it is against parasites, while UV is more eectiveagainst parasites than against viruses.

UV light can inactivate pathogens in a ew tenths o a second, while chlorine requires severalminutes to work.

UV disinection only works on water that is relatively clear, while chlorine can be used todisinect water that is relatively cloudy.

The eectiveness o UV disinection is unaected by the pH and temperature o thewater, while the eectiveness o chlorine is aected by pH, temperature, and the chlorineconcentration in the water.

Table 3.4 shows how long it takes chlorine to achieve a desired level o disinection under a

specic set o conditions. Table 3.5 shows how the eectiveness o chlorine can be aected by pH,temperature, and concentration.

Under the ollowing conditions: Free chlorine residual = 1.0 mg/L (milligrams per liter), pH = 7.0, andtemperature = 20C (68F).

To achieve this levelo Inactivation

This much contact time (minutes) isrequired or this Pathogen

Log Percent Cryptosporidium Giardia Virus

0.5 67 % Ineective 9 0.25 (15 sec)

1.0 90 Ineective 19 0.5 (30 sec)

1.5 96.7 Ineective 28 0.75 (45 sec)

2.0 99 Ineective 37 1

2.5 99.67 Ineective 47 1.5

3.0 99.9 Ineective 56 2

3.5 99.97 Ineective 65 2.5

4.0 99.99 Ineective 75 3

Table 3.4. An Example o the Chlorine Contact Time Requirements orCryptosporidium, Giardia, and Virus Inactivation


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The data presented in Tables 3.4 and 3.5 indicate that you should not rely on chlorine as yourprimary disinectant unless you have used a ltration system that has been certied in accordancewith ANSI/NSF Standard 53 requirements. On the other hand, chlorine is an extremely attractivealternative i you have installed such a ltration system because chlorine is extremely eective againstviral contaminants.

Chlorine is available in gaseous, solid, and liquid orms. We recommend that you avoid using gaschlorine because it is much more corrosive and much more hazardous than the solid (calciumhypochlorite) or liquid (sodium hypochlorite bleach) orms. Chlorine gas is extremely hazardous andhas been used as a chemical warare agent. You should not use chlorine gas unless you have OSHA-approved saety equipment on hand and are extremely amiliar with its use.

Many homeowners and public water systems preer using calcium hypochlorite because, in its solidorm, it is more stable than liquid bleach and is available in higher concentrations. Solid calciumhypochlorite is produced in tablet, pellet, and granular orms. Tablets and pellets are requentlyused in in-line erosion chlorinators. The calcium hypochlorite tablets or pellets are placed insidethe erosion chlorinator; as water fows through the unit, the calcium hypochlorite slowly dissolvesand releases chlorine into the water. Granular products are oten mixed with water to orm aliquid bleach solution that is ed with a metering pump. Due to its high chlorine content, calciumhypochlorite containers should be kept tightly closed and stored away rom combustible materialssuch as oils, uels, and greases.

You can also use sodium hypochlorite (liquid bleach) as your chlorine source. Liquid bleach is

arguably the saest o the chlorine compounds because it is not as concentrated as the other materialsand is less likely to release high concentrations o chlorine gas. However, it is much more susceptibleto thermal decay and you should probably not keep more than a 30- to 60-day supply on hand.Sodium hypochlorite solutions, like solutions o dissolved calcium hypochlorite, are ed with a smallmetering pump.

You should only use chlorine compounds that are certied in accordance with ANSI/NSF Standard60 requirements. This standard, which also applies to any other chemical used to treat potable water,

Based on a 3-log (99.9%) Giardia inactivation

At this water

temperatureAnd this pH

This much contact time (minutes) isrequred i the ree chlorine residual is:

1.0 mg/L 2.0 mg/L

25 C(77 F)

6.5 31 17.5

8.0 54 30.5

5 C(41 F)

6.5 125 69

8.0 216 121.5

Table 3.5. An Example o the Eect that pH, Temperature,and Chlorine Concentration Has on GiardiaInactivation


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assures that your chemical will not pose any chemical or biological threat to you or your amilywhen applied in accordance with manuacturer recommendations. Unortunately, ew i any o theliquid bleaches sold in grocery stores or pool-supply companies carry an NSF label. Although youcan nd a list o approved liquid bleaches on the NSF web site, most o these manuacturers do notproduce small containers o bleach. We try to maintain a list o unlabeled bleaches that meet NSF

requirements. We post this list on our web site, at .I you cannot nd any o the bleach solutions rom our list or the NSFs list, at least avoid theones that contain ragrances or UV stablizers: none o these bleaches are NSF certied.And donot use products designed or use in swimming pools. These products oten contain cyanide-based UV stabilizers.

As stated previously, chlorine is only one o a chemical group known as halogens. The other halogensare bromine, iodine, fuorine, and astatine. Although the other halogens are probably eective viraldisinectants, we recommend that you stick with chlorine because:

1. There is only limited data on the eectiveness o the other halogens. We dont know what levelis needed to kill most pathogens under various conditions or how long it takes or the other

halogens to work.

2. We have not been able to nd any other halogen disinectant that has been certied inaccordance with ANSI/NSF Standard 60 requirements.
http://www.tceq.state.tx.us/goto/bleachhttp://www.tceq.state.tx.us/goto/bleach


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Other Treatment Processes

There are other treatment processes that you may want to consider using to improve the chemicalor aesthetic quality o the water in your home. Some o these (like corrosion control) are more

important than others (like supplemental demineralization).

Corrosion Control

Corrosion control treatment can be very benecial because rainwater is slightly acidic, containsvery ew dissolved minerals, and can be very corrosive. Since plastic pipe is not subject to corrosion,you do not need to consider installing corrosion control treatment i your home is totally plumbedwith plastic pipe. On the other hand, corrosion control treatment is especially important i yourhousehold plumbing was constructed out o thin-walled copper tubing because this material isparticularly susceptible to pinhole leaks. There are several approaches that you can use tocontrol corrosion.

The simplest method or controlling corrosion is to reduce the corrosivity o the untreated waterby periodically adding sodium bicarbonate (baking soda) to your untreated water storage tank.The bicarbonate will increase the alkalinity level (buering capacity) in the water signicantly andraise the pH o the water slightly. One benet o this approach is that, unlike the other alternatives,it will help prevent corrosion in your homes plumbing as well as in your untreated water storagetank. Another benet is that it does not require any special equipment. I you use this approach, werecommend that you apply the ollowing procedure about every three months:

1. Measure the pH o the water in the storage tank.

2. I the pH is 7.4 or higher, youre done.

3. I the pH is between 7.0 and 7.4, add 1 pound o baking soda or every 10,000 gallons o

water or each 0.1 pH unit below 7.4. For example, a tank that contains about 10,000 gallonso water with a pH o 7.1 would require about 3 pounds o baking soda to get the pH up toabout 7.4, while a 5,000-gallon tank would require about 1.5 pounds.

4. I the pH is less than 7.0, add 2 pounds o baking soda or every 10,000 gallons o water, wait acouple o days or the pH to equalize, and then repeat the procedure.

As with any chemical, be sure to use a product that has been certied in accordance with NSFStandard 60. Fortunately, one o the certied products is the Arm & Hammer baking soda you ndat your local grocery store.

To use this approach you need to be able to measure the pH o the untreated water. You can nd pHtest kits at almost any store that sells swimming-pool supplies. We recommend that you select a testkit that will measure both pH and alkalinity. I you use this corrosion control approach, your goal isto keep the pH between 7.0 and 7.5, with an alkalinity level o at least 20 mg/L but not more thanabout 80 mg/L.

I you are supplementing your rainwater system with water rom a public water system, it isimportant to avoid raising the pH above 7.7 or so. At higher pH levels, the calcium carbonatethat is usually present in the water that you get rom a water hauler or public water system mightprecipitate. While this precipitate is not harmul, it may cause the water to be slightly cloudy until


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the next time it rains. You may also be able to eliminate the cloudiness by adding a little acid to thewater to drop the pH back down below 7.7. While we recommend using a product that is certiedunder NSF Standard 60, you can also use acetic acid (white vinegar) rom the grocery store, i theproduct label says that it is sae or ingestion.

Another way to control corrosion is to pass the rainwater through an in-line lter that contains

a bed o calcium carbonate (limestone) pellets, calcium oxide (lime) pellets, or sodium carbonate(soda ash) pellets. As the rainwater passes through the lter bed, it dissolves some o the limestone.The dissolved calcium increases the hardness slightly, which may reduce the likelihood that yourrainwater will corrode your pipes. I you decide to use one o these in-line calcium carbonate ltersin conjunction with a UV disinection unit, be sure to install the lter downstream o (ater) the UVunit to help prevent the ormation o scale in the UV reactor. The UV lamp can get rather warm andcause minerals, such as calcium, to orm scale deposits on the reactor lens.

Yet another way to reduce corrosion rates involves using a metering pump to eed a liquid chemicalcalled zinc orthophosphate. The zinc orthophosphate coats the interior o your pipes and preventsthe sot rainwater rom actually reaching the pipe wall.

As we discussed previously, you should only use chemicals and drinking water additives that arecertied in accordance with ANSI/NSF Standard 60 requirements.

VOC/SOC Adsorption

I you have ollowed our advice, it is very unlikely that your rainwater will contain any signicantamount o volatile organic chemicals (VOCs) or synthetic organic chemicals (SOCs). However, youmay want to install an activated carbon lter to provide an additional level o protection. I you aregoing to install an activated carbon lter, be sure to select one that has been certied or VOC/SOCremoval in accordance with ANSI/NSF Standard 53 and to install it upstream o your chlorinator.Activated carbon adsorbs chlorine, so installing your carbon lter downstream o your chlorinator

will not only remove the chlorine you add, it will reduce the useul lie o the carbon.

Point-o-Use Treatment

Unless something has gone terribly wrong during the primary treatment process, you probablywill not benet much rom installing a point-o-use system (such as a reverse osmosis lter or anactivated carbon lter) at each sink and shower in your home. The only time when you shouldseriously consider using a point-o-use device in a rainwater system is when your homes plumbingsystem was constructed using pipe, aucets, or ttings that contain more than 8.0% lead, or soldersand fuxes that contain more than 0.2% lead. Because rainwater is slightly acidic and very sot, it willeasily leach the lead rom these materials. Excessive lead levels should not be a problem i your home

was constructed ater 1988, because materials produced since that time were required to meet thislow-lead standard. I you do decide to install point-o-use treatment, make sure that it is certiedunder ANSI/NSF Standard 53 to reduce the contaminants that you are targeting.

8/9/2019 Harvesting, Storing and Treating Rain