Distribution System Operation and Maintenance
Pressure and storage
Distribution systems deliver adequate pressure and flow while keeping water safe. Typical minimum is about 20 psi under normal conditions and higher for fire flow; utilities often target 40 to 80 psi. Convert head to pressure with 1 psi = 2.31 ft of water, or 1 ft = 0.433 psi. Storage tanks provide equalization, fire volume, and emergency supply; poor turnover causes stagnation, elevated disinfection byproducts, and nitrification in chloraminated systems.
Pipes, valves, and appurtenances
Know main types, valves (gate, butterfly, check, pressure-reducing), hydrants, meters, and thrust restraint. Main breaks require shutdown, isolation, repair, flushing, and disinfection before return to service. Dead ends and low-flow areas accumulate sediment and biofilm, so flushing programs matter.
Cross-connection control
Backflow prevention uses air gaps, reduced-pressure zone assemblies, double checks, and vacuum breakers. The degree of hazard determines the device. Traps include confusing backsiphonage with backpressure and forgetting that irrigation, boilers, and chemical feed lines are common cross-connections.
Water quality in the system
Monitor chlorine residual, turbidity, and coliforms; manage corrosion with pH and alkalinity adjustment; control lead and copper at the tap. Nitrification in chloraminated systems shows as falling chloramine residual, rising nitrite, and falling pH.
Worked example
A tank water level is 100 ft above a pressure gauge. Static pressure = 100 x 0.433 = 43.3 psi. If the gauge reads 35 psi, expect friction loss or a partially closed valve between the tank and the gauge.