Sprinkler System Water Supply

In NFPA 24—2007, Private Fire Service Main (3.3.11) is defined as “that pipe and its appurtenances on private property (1) between a source of water and the base of the system riser for water-based fire protection systems, (2) between a source of water and inlets to foam-making systems, (3) between a source of water and the base elbow of private hydrants or monitor nozzles, and (4) used as fire pump suction and discharge piping, (5) beginning at the inlet side of the check valve on a gravity or pressure tank.”

A strict interpretation of this definition is that this pipe is for fire protection purposes only, all the way back to the city water main in the street; and that the service for domestic water must be a separate pipe from the city water main with its own valves and fittings.

A less-strict interpretation that is common in southeastern Wisconsin and northeastern Illinois allows one pipe to serve both purposes, provided that it is installed per NFPA 24 and 13; that it is sized to provide the volume required by the sprinkler system plus domestic demand; and that the domestic water supply is tapped off the NFPA-compliant water supply pipe.

The photo shows a 6-inch ductile iron private water supply for both an automatic sprinkler system and domestic water. This short section of pipe passes down through the floor into the soil; is bolted to a ductile iron 90-degree bend below the floor; and is bolted to ductile iron pipe that passes through the foundation wall. It is connected to the plastic water pipe several feet outside the building and to the city water main in the street about 100 feet away. The fiberglass pipe insulation conceals the long anchor rods that replaced several of the flange bolts, and that pass down through the floor, through bolt holes in the 90-degree bend, and into a large mass of concrete that was poured in place below the pipe. This installation was completed by the sprinkler fitters and plumbers working together; was flushed and tested per NFPA standards; and was inspected and approved by both the building department and the fire inspector. The sprinkler system valves, backflow preventer, and riser are in the background. The domestic water supply with its valves, meter, and meter by-pass are in the foreground.

Is this method used in other parts of the U.S., or is it unique to this area?

If you have experience with this type of installation, have there been any problems with water flow pressures or volumes related to domestic use while the sprinklers were flowing water?