Chapter IIReview of Related LiteratureWaterWateris a transparent fluid which forms the world's streams, lakes, oceans and rain, and is the major constituent of the fluids of living things. As achemical compound, awater moleculecontains oneoxygenand twohydrogenatomsthat are connected bycovalent bonds. Water is aliquidatstandard ambient temperature and pressure, but it often co-exists onEarthwith itssolidstate,ice; andgaseousstate,steam(water vapor).Water covers 71% of the Earth's surface.It is vital for all known forms oflife. On Earth, 96.5% of the planet's water is found in seas and oceans, 1.7% in groundwater, 1.7% in glaciers and the ice caps of Antarctica and Greenland, a small fraction in other large water bodies, and 0.001% in theairasvapor,clouds(formed of solid and liquid water particles suspended in air), andprecipitation.Only 2.5% of the Earth's water isfreshwater and 98.8% of that water is in ice andgroundwater. Less than 0.3% of all freshwater is in rivers, lakes, and the atmosphere, and an even smaller amount of the Earth's freshwater (0.003%) is contained within biological bodies and manufactured products. Water on Earth moves continually through the water cycle of evaporation and transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea. Evaporation and transpiration contribute to the precipitation over land. Water used in the production of a good or service is known as virtual water.Safedrinking wateris essential to humans and other lifeforms even though it provides nocaloriesororganicnutrients. Access to safe drinking water has improved over the last decades in almost every part of the world, but approximately one billion people still lack access to safe water and over 2.5 billion lack access to adequatesanitation. There is a clear correlation between access to safe water andgross domestic product per capita.However, some observers have estimated that by 2025 more than half of theworld populationwill be facing water-based vulnerability.A report, issued in November 2009, suggests that by 2030, in some developing regions of the world, water demand will exceed supply by 50%.Water plays an important role in theworld economy, as it functions as asolventfor a wide variety of chemical substances and facilitates industrial cooling and transportation. Approximately 70% of the fresh water used by humans goes to agriculture (http://en.wikipedia.org/wiki/Water).

Water supply systemA water supply system or water supply network is a system of engineered hydrologic and hydraulic components which provide water supply. A water supply system typically includes:1. Adrainage basin(seewater purification - sources of drinking water).2. Araw watercollection point (above or below ground) where the water accumulates, such as alake, ariver, orgroundwaterfrom an undergroundaquifer. Raw water may be transferred using uncovered ground-levelaqueducts, coveredtunnelsor undergroundwater pipesto water purification facilities.3. Water purificationfacilities. Treated water is transferred usingwater pipes(usually underground).4. Water storage facilities such asreservoirs,water tanks, orwater towers. Smaller water systems may store the water incisternsorpressure vessels. Tall buildings may also need to store water locally in pressure vessels in order for the water to reach the upper floors.5. Additional water pressurizing components such aspumping stationsmay need to be situated at the outlet of underground or above ground reservoirs or cisterns (if gravity flow is impractical).6. A pipe network for distribution of water to the consumers (which may be private houses or industrial, commercial or institution establishments) and other usage points (such asfire hydrants).7. Connections to thesewers(underground pipes, or abovegroundditchesin some developing countries) are generally found downstream of the water consumers, but the sewer system is considered to be a separate system, rather than part of the water supply system. (http://en.wikipedia.org/wiki/Water_supply_network)

Water treatmentVirtually all large systems must treat the water; a fact that is tightly regulated by global, state and federal agencies, such as theWorld Health Organization(WHO) or theUnited States Environmental Protection Agency(EPA). Water treatment must occur before the product reaches the consumer and afterwards (when it is discharged again). Water purification usually occurs close to the final delivery points to reduce pumping costs and the chances of the water becoming contaminated after treatment.Traditional surface water treatment plants generally consist of three steps: clarification, filtration and disinfection. Clarification refers to the separation of particles (dirt, organic matter, etc.) from the water stream. Chemical addition (i.e. alum, ferric chloride) destabilizes the particle charges and prepares them for clarification either by settling or floating out of the water stream. Sand, anthracite or activated carbon filters refine the water stream, removing smaller particulate matter. While other methods of disinfection exist, the preferred method is via chlorine addition. Chlorine effectively kills bacteria and most viruses and maintains a residual to protect the water supply through the supply network.

Water distribution networkThe product, delivered to the point of consumption, is calledfresh waterif it receives little or no treatment, ordrinking waterif the treatment achieves thewater qualitystandards required for human consumption.The energy that the system needs to deliver the water is calledpressure. That energy is transferred to the water, therefore becoming waterpressure, in a number of ways: by apump, by gravity feed from a water source (such as awater tower) at a higher elevation, or by compressed air.[1]The water is often transferred from a water reserve such as a large communalreservoirbefore being transported to a more pressurised reserve such as a water tower.In small domestic systems, the water may be pressurised by apressure vesselor even by anunderground cistern(the latter however does need additional pressurizing). This eliminates the need of a water-tower or any other heightened water reserve to supply the water pressure.These systems are usually owned and maintained bylocal governments, such ascities, or other public entities, but are occasionally operated by a commercial enterprise (seewater privatization). Water supply networks are part of the master planning of communities, counties, and municipalities. Their planning and design requires the expertise ofcity plannersandcivil engineers, who must consider many factors, such as location, current demand, future growth, leakage, pressure, pipe size, pressure loss, fire fighting flows, etc. usingpipe network analysisand other tools.As water passes through the distribution system, the water quality can degrade by chemical reactions and biological processes.Corrosionof metal pipe materials in the distribution system can cause the release of metals into the water with undesirable aesthetic and health effects. Release ofironfrom unlined iron pipes can result in customer reports of "red water" at the tap . Release ofcopperfromcopper pipescan result in customer reports of "blue water" and/or a metallic taste. Release ofleadcan occur from thesolderused to join copper pipe together or frombrassfixtures. Copper and lead levels at the consumer's tap are regulated to protect consumer health.Utilities will often adjust the chemistry of the water before distribution to minimize its corrosiveness. The simplest adjustment involves control ofpHandalkalinityto produce a water that tends to passivate corrosion by depositing a layer ofcalcium carbonate.Corrosion inhibitorsare often added to reduce release of metals into the water. Common corrosion inhibitors added to the water arephosphatesandsilicates.Maintenance of a biologically safe drinking water is another goal in water distribution. Typically, a chlorine baseddisinfectant, such assodium hypochloriteormonochloramineis added to the water as it leaves the treatment plant. Booster stations can be placed within the distribution system to ensure that all areas of the distribution system have adequate sustained levels ofdisinfection.Like electric power lines, roads, and microwave radio networks, water systems may have alooporbranchnetwork topology, or a combination of both. The piping networks are circular or rectangular. If any one section of water distribution main fails or needs repair, that section can be isolated without disrupting all users on the network.Most systems are divided into zones. Factors determining the extent or size of a zone can include hydraulics,telemetrysystems, history, and population density. Sometimes systems are designed for a specific area then are modified to accommodate development. Terrain affects hydraulics and some forms of telemetry. While each zone may operate as a stand-alone system, there is usually some arrangement to interconnect zones in order to manage equipment failures or system failures.

Water distribution system operations

Water distribution system maintenance

Definition of Terms