Water Supply and Distribution Systems
Sizing and Pressure
Water supply design balances pipe size, pressure, and flow. Candidates must understand fixture units, developed length, and pressure loss from friction and elevation. Questions test minimum residual pressure at fixtures, the effect of elevation (about 0.43 psi per foot of rise), and why oversized or undersized pipe both cause problems.
Layout and Protection
Supply systems must be protected from contamination (air gaps, backflow preventers), from freezing, and from thermal expansion. Questions often test the location of shutoff valves, the need for a main shutoff, and protection of hose bibs with vacuum breakers. Recirculation systems reduce wait time but add complexity.
Materials and Joints
Supply piping uses copper, PEX, CPVC, and approved galvanized steel. Each has joining rules and pressure ratings. Traps include using a material beyond its temperature or pressure rating, and failing to provide dielectric protection at dissimilar metal connections.
Rule of Thumb
When a question describes low pressure at a distant fixture, check pipe size, developed length, elevation, and whether the system is adequately sized for the fixture units served. When a question describes contamination risk, look for the required backflow protection.
Worked Example
A hose bib without a vacuum breaker can allow backflow into the potable supply if pressure drops. The fix is an approved hose-bib vacuum breaker, which is a simple, low-cost protection required by most codes.