Water Supply and Distribution Systems
Pressure, Flow, and Layout
Water supply design balances pressure, flow, and pipe size. Know the difference between static and residual pressure, and that pressure drops through meters, valves, and elevation. Minimum residual pressure at fixtures is code-specified; excessive pressure requires a pressure-reducing valve. Distribution systems are arranged as a tree or a loop; a loop reduces friction loss and improves pressure at remote fixtures.
Materials and Protection
Know which materials are approved for potable water and where they may be used: copper, PEX, CPVC, and galvanized steel have different temperature and pressure ratings. Questions often test that PEX and CPVC require protection from physical damage and ultraviolet light, and that copper and steel must be separated to prevent galvanic corrosion. Backflow protection is heavily tested: an air gap is the highest protection, a reduced-pressure-zone assembly protects against both backpressure and backsiphonage, and a vacuum breaker protects against backsiphonage only.
Traps in Exam Questions
Watch for questions that confuse water supply fixture units with drainage fixture units, that ignore elevation loss (about 0.43 psi per foot of rise), and that assume a larger pipe always improves pressure - oversized piping can increase stagnation and water age. Also remember that a water heater's temperature and pressure relief valve discharge must terminate safely, not be capped or plugged.
Worked Example
If a fixture needs 8 psi and sits 20 feet above the meter, the elevation loss is 20 × 0.43 ≈ 8.6 psi. Add friction loss (say 5 psi) and the required supply pressure is about 8 + 8.6 + 5 ≈ 21.6 psi at the meter outlet - a useful rule of thumb for pressure checks.