Water Distribution
Pressure, head, and flow
Distribution questions reward fluency with the pressure-head relationship: 1 psi = 2.31 ft of water, and 1 ft of water = 0.433 psi. Static pressure at a point equals the elevation head relative to the hydraulic grade line. Pumps add head; friction consumes it. Hazen-Williams is the usual friction formula, and the C-factor falls as pipe ages. Main velocity is generally kept between roughly 2 and 5 ft/s: too low causes sedimentation and water age, too high causes head loss and surge.
Operations and water quality
Know storage (elevated tanks and reservoirs that equalize demand and provide fire flow), valves (isolation, altitude, pressure-reducing), hydrants, and backflow prevention. Cross-connection control uses air gaps, reduced-pressure-zone assemblies, and double-check valves; an air gap is the only true isolation. Distribution water quality depends on residual maintenance, flushing, storage turnover, and eliminating dead ends. Nitrification in chloraminated systems, disinfection byproduct formation, and biofilm growth are all water-age problems.
Traps
Confusing psi with feet of head; using total dynamic head when only static head is asked; forgetting that a pressure-reducing valve lowers pressure but not total energy; and assuming a check valve is a backflow assembly. Items often ask which device protects against both backsiphonage and backpressure: the RPZ assembly.
Worked example
A tank water surface sits 115 ft above a service connection. Static pressure = 115 ÷ 2.31 = 49.8 psi, about 50 psi, before any friction or building elevation loss.