Water Distribution
Pressure, storage, and public-health protection
Distribution questions blend hydraulics with water-quality protection. Learn pressure and head (1 psi ≈ 2.31 ft of water), friction loss and C-factors in Hazen-Williams, pump curves, storage volume and turnover, and fire-flow demand. Lower C-factors mean rougher pipe and more head loss; higher flow always costs pressure. Pressure drives customer service and fire protection but also causes main breaks, while storage equalizes demand, supplies fire volume, and helps keep residual in the system. Know the cross-connection hierarchy: air gaps and reduced-pressure-zone assemblies for high hazard, double checks and vacuum breakers for lower hazard, plus annual backflow testing and containment versus isolation.
Quality traps include sampling at representative worst-case sites, flushing dead ends to control water age and disinfection by-products, and maintaining residual after main repairs and disinfection. Watch pressure-versus-flow confusion, psi-versus-feet conversions, and valve or hydrant operation that unintentionally isolates customers.
Worked example: a tank water level is 100 ft above a service connection. Static pressure = 100 ÷ 2.31 ≈ 43 psi. Subtract friction loss along the main; if that is 10 psi, the customer sees about 33 psi.
Rule of thumb: maintain at least 20 psi at all points under normal and fire-flow conditions; below that, contamination intrusion risk rises.