Water Supply and Distribution
Water Supply and Distribution tests sizing, pressure control, backflow protection, materials, joints, valves, and testing. The exam expects you to connect fixture demand to pipe size and to recognize when a pressure-reducing valve or backflow preventer is required.
Pressure
Static pressure above 80 psi requires a pressure-reducing valve. Residual pressure must be adequate at the most remote fixture; flushometer fixtures need more pressure than tank-type water closets. Elevation changes affect pressure, so a street pressure reading alone is not enough for a tall building.
Backflow protection
The degree of hazard determines the device. An air gap provides the highest protection. A reduced-pressure zone assembly is used for high-hazard connections, while a pressure vacuum breaker or double check valve may suit lower hazards. Hose bibbs need vacuum breakers. Backflow assemblies must be accessible for testing and maintained.
Sizing and materials
Sizing uses fixture units, developed length, elevation, and pressure loss. Approved materials and joints must match the application. Water hammer arrestors are required where quick-closing valves can cause shock. Water piping must be tested at 100 psi or working pressure, whichever is greater, for 60 minutes.
Worked example
A building has 92 psi static pressure at the street and no pressure-reducing valve. Because 92 psi exceeds 80 psi, a PRV is required. The downstream setting must still leave enough residual pressure for the highest and most remote fixtures after elevation and friction losses are calculated.
Traps that cost marks
Using street pressure without subtracting elevation loss is a common error. Another is choosing a double check valve for a high-hazard connection when an RPZ or air gap is required. Do not forget hose bibb vacuum breakers.