Water Supply and Distribution
Water Supply and Distribution
This domain tests sizing, pressure, distribution layout, and protection of the potable supply. The exam expects you to balance available pressure against elevation, friction, and fixture demand, and to choose materials and fittings approved for potable water.
Core rules
- Size water piping from fixture-unit demand and developed length, then verify residual pressure at the farthest fixture. Static pressure is not flowing pressure; subtract meter loss, elevation loss (0.434 psi per foot of rise), and friction.
- Keep velocities reasonable to avoid noise and erosion. Support pipe at required intervals, protect it from freezing, and provide access to valves and cleanouts.
- Install backflow protection at the service and at any connection that could reverse flow. Thermal expansion control is required on closed systems.
- Water hammer arrestors are needed near quick-closing valves and at groups of fixtures where shock is likely.
Worked example
Street pressure is 60 psi. The meter and service lose 8 psi, the highest fixture is 20 feet above the meter (20 x 0.434 = 8.7 psi), and the fixture needs 15 psi flowing. Remaining for pipe friction is 60 - 8 - 8.7 - 15 = 28.3 psi. If the longest developed run has more friction loss than 28.3 psi at the design flow, increase pipe size or reduce developed length.
Traps
Do not use static pressure as the design pressure. Do not ignore the elevation of the highest fixture. Do not size a long run from fixture count alone without checking friction loss. Do not install a check valve without planning for thermal expansion.