Chapter 2 of 622% of exam

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.

Water service pipe
Carries water from the meter or source to the building supply and must be sized for total demand plus any future load.
Minimum supply pressure
The distribution system must deliver adequate pressure at the fixture; low pressure or an oversized fixture count requires larger pipe.
Provide potable water
Only approved, potable-rated piping and fittings may be used in the water distribution system.
2022 California Plumbing Code (CPC) §604.0
Separate from drainage
Water piping must be kept separated and protected from drainage piping to avoid contamination.

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.

Water supply fixture unit (WSFU)
A weighting value for each fixture that reflects its flow rate and frequency of use, used to estimate probable simultaneous demand.
Total and convert
Add the WSFU of all fixtures, then use a code table or chart to convert to design flow in gallons per minute.
Consider developed length
Longer runs lose more pressure to friction, so a longer developed length may require a larger pipe for the same flow.
Sizing basis
Pipe sizing is based on available pressure, friction loss, elevation, and demand; the code provides sizing tables for this purpose.
2022 California Plumbing Code (CPC) §610.0

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.

High pressure limit
Where static water pressure exceeds 80 psi, an approved pressure-reducing valve must be installed to reduce it.
2022 California Plumbing Code (CPC) §608.2
Pressure-reducing valve (PRV)
Reduces incoming pressure to a set downstream value that protects piping and fixtures from damage.
Thermal expansion
A closed system created by a PRV or check valve requires an expansion tank or relief so heated water can expand safely.
Water hammer
Quick-closing valves cause pressure surges; arrestors or air chambers are used to absorb the shock.

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.

Air gap
A physical vertical separation between a supply outlet and the flood level rim of a receptor; it is the most reliable backflow protection.
2022 California Plumbing Code (CPC) §603.0
Reduced pressure principle (RP) assembly
A testable assembly with two check valves and a relief valve used for high-hazard connections under backpressure or back-siphonage.
Double check (DC) assembly
Two check valves in series used to protect against low-hazard backpressure or back-siphonage.
Pressure vacuum breaker (PVB)
Protects against back-siphonage only and must be installed above the highest downstream outlet, commonly on irrigation.
Match to hazard
The type of assembly must match the degree of hazard, with air gap or RP required for high-hazard situations.

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.

Approved water piping
Common approved potable materials include copper, CPVC, PEX, and galvanized steel where permitted; each must be listed for the use.
2022 California Plumbing Code (CPC) §604.1
Hanger and support spacing
Horizontal piping must be supported at intervals set by the code for each material so it does not sag or strain joints.
2022 California Plumbing Code (CPC) §313.0
Vertical support
Vertical piping must be supported at each floor or at code intervals to carry its own weight.
Protect the pipe
Supports must not react adversely with the pipe; dissimilar metals are isolated to prevent galvanic corrosion.
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Last updated: July 2026

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