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

Chapter 7 -- Min i mum Construction Standards forFinished Water Storage Tanks and Reservoirs7.0. General Design and Construction Standards7.0.1. AWWA Standards for Unpressurized Tanks and ReserviorsUnless otherwise noted in this rule, unpressurized tanks and reservoirs forfinished water storage shall be designed and constructed in accordance with thelatest edition of the American Water Works Association (AWWA) standards, asfollows:Welded Steel Tanks for Water StorageCoatings for Steel Water Storage TanksFactory Coated Bolted Steel Tanks forWater StorageAutomatically Controlled ImpressedCurrent Cathodic Protection for the Interiorof Steel Water TanksWire and Strand Wound Circular, PrestressedConcrete Water TanksCircular Pre-stressed Concrete Water Tankswith Circumferential TendonsAWWA Standard D100AWWA Standard D102AWWA Standard D103AWWA Standard D104AWWA Standard D110AWWA Standard D1157.0.2. Parameters for Unpressurized Tanks and Reservoirs for Finished WaterStorageThese parameters should be considered during the design of unpressurized tanksand reservoirs for finished water storage.a. Tank design should be part of a unified long range, engineering designthat includes wells, treatment plants, high service pumps, booster pumps,and distribution mains. Since tanks have an approximate useful life of 50years, the design should consider future growth, including the elevation ofareas likely to be developed during the useful life of the tank. Currentservice area and future service area should be divided into appropriatepressure zones with operating pressures between 35 psig and 100 psig.All of these items should be reflected in the design to ensure the tank willnot become obsolete during its useful life.b. The tank should be designed to maintain water temperature above 32˚ Fduring the winter weather that would result in the lowest storage watertemperature during a seven-day period taken from the most recent 100-year period of weather data or statistically calculated as a 100-year returnfrequency. An energy balance should be calculated using the followingAug. 29, 2003Page 133