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278 Chapter 8 Pumping, Storage, and Dual Water Systems
supply lines, increased fire protection, and more uniform pressures in the distribution
system.
Storage facilities should have sufficient capacity, as determined from engineering
studies, to meet domestic demands and, where fire protection is provided, fire flow de-
mands. The recommended standards for sizing a water storage tank or reservoir as stated in
the Recommended Standards for Water Works, 2007 Edition (Health Research, 2007; often
referred to as the Ten-States Standards) are as follows:
1. Fire flow requirements established by the appropriate state Insurance Services
Office should be satisfied where fire protection is provided.
2. The minimum storage capacity (or equivalent capacity) for systems not providing
fire protection shall be equal to the average daily consumption. This requirement
may be reduced when the source and treatment facilities have sufficient capacity
with standby power to supplement peak demands of the system.
3. Excessive storage capacity should be avoided to prevent potential water quality
deterioration problems.

EXAMPLE 8.6 TOTAL WATER STORAGE VOLUME
For a steady gravity supply equal to the maximum daily demand, a 4-h fire supply at 8,000 gpm
3
(0.505 m /s 505 L/s), and no particular hazard to the supply works, find the storage to be pro-
3
vided for a city using an average of 7.5 MGD (0.328 m /s 328 L/s) of water.
Solution 1 (U.S. Customary System):
The equalizing storage is 15% of average daily consumption:
0.15 7.5 MG 1.13 MG

The fire reserve is 8,000 gpm for 4 hours:
6
(8,000 gal/min 4 h 60 min/h) 10 1.92 MG
The resulting subtotal is 1.13 1.92 3.05 MG.
Because the emergency reserve is one-fourth of the total storage, the subtotal is three-fourths
(0.75) of the total storage. Therefore,
Total storage 3.05 0.75 4.1 MG

Solution 2 (SI System):
3
3
3
0.328 m /s 0.328 24 60 60 m /d 28,387 m /d
The equalizing storage is 15% of average daily consumption:
3
0.15 28,387 m 4,258 m 3
3
The fire reserve is 0.505 m /s for 4 hours:
3
(0.505 m /s)(4 60 60 s) 7,269 m 3
3
The resulting subtotal is 4,258 7,269 11,527 m .
Because the emergency reserve is one fourth of the total storage, the subtotal is three fourths
(0.75) of the total storage. Therefore,
Total storage 11,527 0.75 15,369 m 3