Distribution Systems, Storage, and Cross-Connection Control
Distribution is hydraulics plus public health. Understand pressure maintenance (typically 20 psi minimum under normal conditions and higher for fire flow), head loss from friction, pipe sizing, loops vs. dead ends, and flushing to control water age, disinfectant residual, DBPs, and sediment. Storage: elevated tanks, ground storage, hydropneumatic tanks, overflow, altitude valves, and mixing to avoid stagnation and stratification. Know backflow concepts: backpressure vs. backsiphonage, air gap (best), RPZ, double check, and vacuum breakers, plus cross-connection surveys and containment vs. isolation.
Traps: believing any check valve is adequate backflow protection; confusing pressure with flow; ignoring that dead ends and oversized mains raise water age; and forgetting that storage tanks need inspection, venting, and security.
Rule of thumb: protect the system at the service connection with an appropriate assembly, and eliminate or isolate every actual or potential cross-connection. Worked example: a facility with a boiler feed line and chemical injection needs an RPZ at containment because both backpressure and backsiphonage are possible; a simple double check is not enough where a health hazard exists.