Water Distribution
Pressure, storage, and water age
Distribution systems are judged by pressure, residual maintenance, and water quality. Keep positive pressure at all points under normal and fire-flow conditions; storage tanks must turn over to avoid stagnation. Long dead ends, oversized mains, and low demand create high water age, which decays disinfectant residual and can promote nitrification in chloraminated systems. Flushing, looping, and valve and hydrant exercise are the standard controls.
Cross-connection control
Backflow is the reverse flow of nonpotable water into the public system. Protect with air gaps, reduced-pressure-zone assemblies, and testable devices; test annually and maintain records. A common trap is assuming a double check is adequate for a high hazard, or forgetting that a loss of pressure can create backsiphonage.
Main breaks and repairs
Use standard disinfection and flushing after repairs: isolate, repair, flush, disinfect, and sample before returning to service. Bacteriological sampling follows the total coliform rule; a positive routine sample triggers repeat samples and investigation.
Worked example
Volume of an 8-inch main 1,000 ft long: radius 0.333 ft; area = πr² ≈ 0.349 ft²; volume ≈ 349 ft³; times 7.48 gal/ft³ ≈ 2,610 gallons. That tells you how much flush water and disinfectant contact volume you are dealing with.