Acceptable Water Supplies for Sprinkler Systems
An acceptable water supply for a Sprinkler System must provide sufficient flow and pressure for the required duration, without the need for any human intervention, to meet the most hydraulically demanding area in the facility, including any hose stream allowances. Additionally, the water supply must also be reliable.
The selection of appropriate water supplies must not be overlooked and the paragraphs below are a quick review on the acceptable water supplies to be used for Sprinkler Systems designed in accordance with NFPA 13. The seven acceptable water supplies for sprinklers systems are listed below. An acceptable water supply can be one or a combination of any of the following methods.
- Connection to a Public or Private Waterworks System
The connection of a sprinkler system to a public or private waterworks system is deemed the first choice since they are generally considered to be reliable, accessible and can accommodate the demand for a wide range of sprinkler systems. However, the capacity of such a connection needs to be evaluated using a water flow test or other approved method. NFPA 13 mandates that the flow test be conducted not more than 12 months prior to the submittal of the working plans. The most common concern in determining the capacity of a public or private waterworks is the adjustments that need to be factored in to accommodate fluctuations or deterioration in the water supply capacity over seasonal usage, drought conditions, future developments etc. Therefore, it is recommended to have a safety factor be incorporated into the water supply evaluations, to mitigate the above-mentioned variations.
In conditions where the available water supply is not adequate to meet the required system demand and pressure, a listed Fire Pump that is installed in accordance with NFPA 20 is an acceptable water supply. The Fire Pump cannot create more water than that is available from a given water source, but it can increase pressure to a Sprinkler System from an existing water supply. The concern discussed earlier related to satisfactorily determining the capacity of available water supply and the application of a safety factor to the evaluations are applicable if the water supply is from a public waterworks system. The Fire Pump can also have its suction taken from a reservoir, pond, lake, river, cistern, well, etc.
- Connection to a water storage tank
A connection to a water storage tank at grade or below grade, installed in accordance with NFPA 22 and filled from an approved water source is an acceptable water supply. This type of arrangement is most often accompanied with the use of a fire pump, to increase the pressure of the available water source, to meet the system demand. This type of water supply can be reliable when the tank is filled to the maximum capacity. However, over time, the adequacy and dependability of the water source for filling the tank is also of primary importance. The water supply source that will be used to fill the tank must be capable of filling the minimum required fire protection volume within the tank in a maximum of 8 hours.
- Pressure Tanks
A Pressure Tank that is installed in accordance with NFPA 22 is also an acceptable water supply. A Pressure Tank contains both water and air under pressure and should have enough air to discharge the water from the tank at the necessary rate. Since a Pressure Tank is required to have provisions to maintain the air pressure automatically, it is required to be monitored by the fire alarm system for low air pressure trouble signal in order to increase the reliability of the water source. Since Pressure Tanks larger than 9000 gallons are rarely available however, the use of a Pressure Tank as a water supply is limited.
- Gravity Tanks
An elevated tank (or Gravity Tank) installed in accordance with NFPA 22 is an acceptable water supply. Gravity Tanks are now uncommon for private water supplies but are still used as part of a reliable waterworks system. The availability of a wide variety of fire pumps with other water supplies have made them preferable to the dated Gravity Tank method for use as a sprinkler system water supply.
- Penstocks, Flumes, Rivers or Lakes
Water supply sources such as penstocks, flumes, rivers, and lakes are acceptable water supplies when used in combination with listed fire pumps. However, these sources must be arranged to avoid mud and sediment and other foreign material in the system piping. Such sources must, therefore, be provided with an approved double removable screens or approved strainers installed on the water intake piping. A major concern while selecting a naturally occurring water source is their reliability and ability to meet the system demand throughout the year, accounting for seasonal fluctuations, as well as low water levels and ice conditions. Therefore, the Authority Having Jurisdiction should be consulted before deciding to use a naturally occurring water source as the water supply for a sprinkler system.
- Recycled or Reclaimed Water Source
There have been efforts made to move towards more sustainable use of water sources by utilizing recycled or reclaimed water and captured rainwater for a sprinkler system in lieu of potable water. The recycled water has to be stored in any of the acceptable methods as discussed above, such as a storage tank, pond etc., ensuring that sufficient capacity is available at all times. However, recycled water obtained from an industrial process might have contaminants that are combustible or contaminants that could accelerate corrosion etc. Therefore, it is necessary to perform a detailed analysis of the water source to determine if contaminants might be present in the recycled water and to confirm any contaminants will not affect the operation of the sprinkler system in any manner. Upon successful completion of such an analysis, the use of recycled or reclaimed water will be an acceptable water supply source.
PLC Fire Safety Engineering has the knowledge and expertise in determining and evaluating the options for your Sprinkler System Water Supply.