Water Distribution Systems
Pressure and pathways
A distribution system is judged on three things: adequate pressure, adequate flow, and acceptable water quality at the tap. Minnesota rules and the Ten States Standards call for a minimum of 20 psi under normal and fire-flow conditions; below that, contamination can enter through leaks and cross connections. Pressure is not flow: a system can hold 60 psi static and still fail a fire-flow test because of undersized mains, closed valves, or heavy friction loss.
Know the hardware: transmission and distribution mains, looping versus dead ends, gate and butterfly valves, blow-offs, hydrants, thrust blocks and restrained joints, meters, elevated and ground storage, hydropneumatic tanks, and booster pumps and pressure-reducing valves that define pressure zones. Storage supplies fire volume, emergency reserve, and contact time, but oversized or poorly mixed tanks create stagnant water, low residual, and disinfection byproducts.
Cross-connection control is heavily tested. An air gap is the only true backflow prevention; a check valve is not. Know the devices - RPZ, double check, pressure vacuum breaker, atmospheric vacuum breaker - and where each is allowed. New and repaired mains are disinfected, flushed, and sampled before service. Dead ends are flushed on schedule because residual drops as water age increases.
Rule of thumb: 1 psi = 2.31 feet of head. A tank with 100 ft of water above a tap delivers roughly 100 ÷ 2.31 ≈ 43 psi before friction loss is subtracted.