ACROSS THE COUNTRY, more and more homeowners are considering home fire sprinklers to provide the ultimate level of life safety. One of the common questions that arises has to do with the types of water supplies that can be used with home fire sprinklers.
NFPA 13D, Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes, allows for a plethora of prescriptive options, including municipal water supplies, tank and pump arrangements, and even well water. There are pros and cons to each of these arrangements, and the designer and homeowner should look at them on a case-by-case basis.
The use of a municipal water supply is a tried-and-true source for fire protection water. This is the most common mechanism for supplying water to commercial sprinkler systems, often supplemented with a fire pump. Municipal water supplies can be a great source for NFPA 13D systems as well. Many municipal water supplies maintain system pressures sufficient enough to meet the demands of an NFPA 13D system without the need for a pump, and they supply well in excess of the minimum 10-minute water supply outlined in the standard. There can be challenges with “connection” fees and water metering in certain jurisdictions, however, and where these challenges present themselves, it may be prudent for the designer and homeowner to look into an alternative water supply source.
Another common water supply source for the commercial sprinkler system that translates well into the NFPA 13D application is a water storage tank. Due to the relatively low demand required by NFPA 13D, most tanks supporting NFPA 13D sprinkler systems will be 500 gallons or less, unless an extended water supply duration or additional sprinklers are considered in the hydraulic calculations for enhanced property protection. These tanks are not required to comply with NFPA 22, Water Tanks for Private Fire Protection, and therefore can be highly cost-effective. Tanks of this size typically take up less than 16 square feet of floor area in a garage, basement, or other utility space, and are supported by small pumps to provide the needed flow and pressure. These pumps are not required to comply with the provisions in NFPA 20, Installation of Stationary Pumps for Fire Protection, which makes them cost-effective and readily available to designers and installing contractors to use in projects. In addition to tank and pump arrangements, elevated tanks and pressure tanks are also expressly permitted by NFPA 13D.
The standard also permits the use of well water as a water supply, a feature unique to NFPA 13D. In this option, the source can be a combination of the water in the well, including the refill rate, plus the water in a holding tank. When selecting a well as the source for home fire sprinklers, it is important that designers take into account seasonal and climatological groundwater recharge when determining if the well is capable of meeting the system demand. Using the refill rate calculated the day after a large rainstorm will allow the groundwater source to fill the well more expediently than it would after 30 days without rain.
These prescriptive sources aren’t the only potential options for water supply sources. Residential sprinkler systems are also supplied by raw water sources like retention ponds and lakes, as well as swimming pools. These sources may require special design features such as strainers or anticorrosive components, and would always require approval from the authority having jurisdiction.