Every sprinkler system requires at least one automatic water supply of adequate pressure, capacity, and reliability. The water supply needs to be capable of supplying all sprinklers that might operate during a fire, while also providing water that will be needed for the fire department. Minimum water supply requirements can be found in various National Fire Prevention Association (NFPA) standards, particularly Standard No. 13. Determining the number of sprinklers that might operate during a fire depends on many variables, including:

• Fire hazards in your building or unit that result in the operation of multiple sprinklers. Of particular concern are hazards with the potential to cause flash fires and materials that rapidly generate high heat;
• Building conditions such as high ceilings, unprotected floor openings, and large undivided areas can result in the operation of a large number of sprinklers;
• The arrangement of materials or operations. Obstructions to the distribution of water from sprinklers may be caused by storage in racks or shelving, large equipment, or similar obstructions;
• Fire originating in areas of the building without sprinklers and spreading into a sprinkler area can result in many sprinkler openings; and
• Low initial water pressure can result in many sprinklers operating during a fire. At a pressure of 15 pounds per square inch, a standard sprinkler will discharge about 20 gallons per minute (GPM). At higher pressures, the discharge will increase. Therefore, the greater the amount of water discharged when the first sprinkler operates, the better the chances of controlling a fire with only a few sprinklers.

NFPA Standard No. 13 provides guides to water supply requirements for sprinkler systems using the pipe schedules provided in the standard. The guides are based on the hazards of occupancy and vary from 500-1,500 GPM and higher.

Required periodic inspection of the automatic sprinkler system should be conducted to include a main drain flow test by qualified persons. This will ensure proper operation and the availability of adequate water supply for use in the event of a fire. Records of all activities should be maintained.