Distribution System Design, Operation, and Maintenance
Distribution System Design, Operation, and Maintenance tests whether you can keep treated water safe from the plant to the tap. Expect questions on pressure, storage, main sizing, valves and hydrants, flushing, disinfectant residual, main breaks, and bacteriological sampling.
Core rules and concepts
- Maintain positive pressure. Federal and state practice uses 20 psi as a minimum during normal operations; below that, contamination can enter through leaks.
- Storage equalizes demand, provides fire flow, and maintains pressure. Tank turnover matters: long storage time can degrade residual and increase water age.
- Main sizing depends on peak demand, fire flow, and head loss. Dead ends and oversizing increase water age.
- Flushing removes sediment and stale water. Unidirectional flushing uses a controlled velocity and a directed flow path.
- Main breaks require isolation, repair, disinfection, and bacteriological sampling before return to service.
- Valve and hydrant exercise prevents seized assets and confirms isolation capability.
Worked example
A storage tank water surface is 100 ft above a service connection. Pressure at the connection from elevation alone is 100 ft ÷ 2.31 ft/psi = 43.3 psi. If the connection is 30 ft higher, the available pressure drops to (100 − 30) ÷ 2.31 = 30.3 psi. Subtract friction loss to estimate actual operating pressure; elevation alone is not the whole answer.
Traps
Assuming pressure is the same everywhere in a pressure zone; ignoring friction loss; flushing without a velocity or flow target; returning a repaired main to service without sampling; letting storage stagnate; confusing fire flow with normal peak demand.