Design Guide for Community Water Systems - The Water, Sanitation ...

7.3. Distribution StorageThese requirements are in addition to the applicable requirements listed insubsections 7.0. and 7.1.7.3.1. Minimum PSIG at Normal Ground ElevationDistribution storage shall be designed and constructed in conjunction withproduction facilities, pumping facilities, and distribution mains to provide aminimum of 35 psig pressure at the normal ground elevation at every point ofthe distribution system during all conditions of design flow. Normal operatingconditions include extended drought usage and diurnal peak flow.7.3.2. Working Pressure PSIG at Normal Ground ElevationDistribution storage should be designed and constructed in conjunction withproduction facilities, pumping facilities, and distribution mains to provide aworking pressure of 60 psig at the normal ground elevation at every point inthe distribution system during all normal operating conditions except fireflow.a. Areas with elevation differences of more than 150 feet should be dividedinto multiple pressure zones so that each zone has pressure between 35and 100 psig.b. Multiple pressure zone systems should have separate storage facilities foreach zone and should be equipped so that water can be transferredbetween zones with pump stations and pressure control valves.c. Each public water system shall be designed to maintain normal systempressures and flows with any storage facility out of service formaintenance or should have at least two storage tanks or reservoirs so thatremoving a tank or reservoir for maintenance will not disrupt distributionsystem pressure.7.3.3. Distribution Storage ControlsDistribution storage facilities shall be equipped with adequate controls tomaintain levels in the tanks/reservoirs.a. Level indicating devices should be located at a central location.b. Pumps should be controlled from tank levels with the signal transmittedby telemetering equipment when any appreciable head loss occurs in thedistribution system between the pump and the storage structure. Pressurecontrol valves (usually installed on the discharge line and pump to wasteline with a control system that opens and closes these valves simultaneousto control pressure surge/water hammer) should be installed on pumpswhen pumps and storage facilities are not adjacent.c. Overflow and low level warnings or alarms should be located at places inthe community where these will be under responsible surveillance 24hours per day.Aug. 29, 2003Page 143