Water Supply and Distribution
The water supply system delivers safe potable water at adequate pressure to every fixture while preventing contamination of the public supply. This chapter covers service and distribution sizing, pressure control, backflow protection, approved materials, and pipe support.
Water Service and Distribution
The water service is the pipe from the public main or private source to the building, and the distribution system carries water from that point to the fixtures. Piping must be sized so every fixture receives enough flow and pressure even when several are used at once.
Pipe Sizing by Fixture Units
Supply pipe is sized using water supply fixture units (WSFU), a value assigned to each fixture that represents its probable demand. Fixture units are totaled and converted to a peak flow in gallons per minute, then a pipe size is selected for the available pressure and developed length.
Pressure and Pressure-Reducing Valves
Water pressure that is too high stresses piping, fixtures, and appliances and causes noise and leaks. Where static pressure exceeds the code limit, a pressure-reducing valve (PRV) is installed to lower it to a safe working range.
Backflow and Cross-Connection Control
A cross-connection is any point where the potable supply can be contaminated by nonpotable water flowing backward, either by back-siphonage or backpressure. The code requires an approved air gap or backflow prevention assembly matched to the degree of hazard.
Approved Materials and Pipe Support
Only piping materials approved for potable water may be used, and all piping must be supported at intervals that prevent sagging, stress, and misalignment. Support spacing depends on the pipe material and whether the run is horizontal or vertical.
Last updated: July 2026