2Distribution System Layout Layout of water distribution system is a function of:source of water supplytopography of distribution areavariation in water consumption
3Source of Water Supplywater is supplied at one point (i.e. treatment plant)distribution storage (elevated tank or ground-level tank plus booster pump) is required in remote areas to maintain water pressurewater is supplied at several points (wells)storage capacity is reduced and pipe sizes required are smaller.
4Topography water is supplied at high elevation it flows by gravity through the water network.water is supplied at low elevationmust be pumped up into the water network (pipes and storage).
5Water Consumptionis a function of residential, commercial and industrial demands.planning and zoning is applied to control variations in water consumption.Climate and economical aspects could also influence the layout of a water distribution system.
6The objective of an engineer designing a water distribution system is to provide a stable hydraulic gradient to maintain adequate pressure throughout the service area and enough pumping and storage capacities to meet emergency demands.The following figure shows simplified water distribution systems which illustrate the basic principles of design.
9Quantitythe water source plus the storage facilities must be able to provide enough water to meet both current and future demands (ten years ahead).records of average daily, peak daily, peak hourly rates of consumption of the past ten years are needed, beside other factors related to community growth, to project the future needs.
10Intake Capacitysurface water intakes must be large enough to deliver enough water to meet municipal use and treatment plant needs during any day of peak demand.if storage is not available, water intake capacity must be large enough to meet fire demand, maximum hourly flow, and inplant process needs at the same time.
11Pumping CapacityLow-lift pumps transport water from the source to the treatment plant.High-lift pumps transport water from the treatment plant to the distribution system.Well pumps deliver water to the treatment facilities or directly to the distribution system.Booster pumps are needed to increase pressure in the distribution system of large communities or in areas with widely varying elevations.Pumping stations must have enough capacity to provide the amount of water at flow and pressure rates needed to meet both daily and hourly peak demand plus fire flow.Pumping stations must be reliable through duplication of units, standby equipment, and alternate sources of power
12Piping NetworkArterial and secondary feeder mains must be designed to supply water service for 40 or more years after installation.Actual lifetime of pipes of mains under normal conditions is 50 to 100 years.Sub-mains must be at least 6 inches in diameter in residential districts and 8 inches in important districts.Distribution lines are laid out in gridiron patternAvoid dead-endsAdequate number of valves must be installed to allow shutoff in case of emergencyValves should be located in a way so that no more than one block will be out of service in case of emergency.