Uniform Plumbing Code - Water Supply
What this domain covers
The water supply domain tests potable water protection, cross-connection control, pressure, sizing, materials, valves and testing. Many questions ask you to select a backflow method for a described hazard or to check whether a system has adequate pressure and capacity.
Core rules
- Only potable water may supply fixtures unless an approved separate system is provided. Protect the potable system from cross-connections using the method appropriate to the hazard: air gap, reduced-pressure zone backflow preventer, double check valve assembly, pressure vacuum breaker or atmospheric vacuum breaker.
- Maintain adequate pressure at fixtures under flow. Excess static pressure requires a pressure-reducing valve, and a closed system needs thermal expansion control.
- Size water piping by water supply fixture units, developed length, pressure and allowable friction loss, using the UPC sizing tables. Do not size by guess or by fixture count alone.
- Use approved materials and joints, keep valves accessible, provide water hammer arrestors at quick-closing valves, and test the system before concealment.
- A typical hydrostatic test is 100 psi for 15 minutes, or the working pressure if higher, with no loss.
Worked example
A new irrigation tap is taken from the potable service, and the system includes chemical injection. This is a high-hazard cross-connection. A double check valve assembly is not sufficient; an air gap or reduced-pressure zone backflow preventer must be installed, protected from freezing and testing, and tested by a qualified tester. The reasoning is that fertilizer or pesticides can back-siphon into the potable main.
Traps that cost marks
Selecting a double check valve for a high hazard; ignoring static pressure above the reduction threshold; omitting an expansion tank on a closed system; sizing from fixture count without developed length; and burying or blocking access to a backflow preventer.