Suction tanks supplying fire pumps are another acceptable source of water for a sprinkler system. A fire protection engineer or similar expert sizes the tank based on the total volume of water required to meet the demands of the fire sprinkler system for the duration of time the engineer expects the sprinklers to operate. The engineer measures the demand of the sprinkler system in gallons per minute and the duration in minutes. If there's a way for the fire department to tap into the supply, the engineer adds that volume of water to the tank size. If a fire pump pressurizes the system, the pressure requirements of the fire sprinkler system and the fire department’s use are primary considerations for pump selection.
Suction tanks are usually made of steel, and standard sizes range from 50,000 to 1,000,000 gallons.
To prevent freezing and subsequent pump failure, such tanks circulate heated water or use embedded coils.