Water Distribution
What the exam tests
Water Distribution tests how treated water is stored, pumped, and delivered while preserving pressure, quality, and public health protection. Questions target pressure, chlorine residual, cross-connection control, main repair and disinfection, sampling, flushing, and recordkeeping.
Core rules and concepts
- Static pressure conversion: 1 psi = 2.31 ft of water. Pressure falls with elevation and friction loss; minimum residual pressure and fire-flow requirements are set in state design standards.
- Distribution systems must maintain a disinfectant residual; free chlorine is common, but chloramines require careful ammonia control and nitrification monitoring.
- Cross-connection control uses air gaps, reduced-pressure-zone backflow preventers, and testable devices; annual testing and records are essential.
- New and repaired mains require flushing, chlorination, retention, and bacteriological sampling before return to service.
- Coliform sampling sites must represent the system; repeat samples and special samples follow triggered monitoring rules.
Worked example
A storage tank’s high-water elevation is 120 ft above a hydrant. Ignoring friction, static pressure at the hydrant is 120 ÷ 2.31 = 51.9 psi. If the hydrant is 30 ft higher than the tank’s low-water level, pressure at low water is 90 ÷ 2.31 = 39.0 psi. That lower value governs customer service and fire-flow checks. If measured pressure is much lower than calculated, look for closed valves, heavy demand, or pipe roughness rather than assuming the gauge is wrong.
Traps that cost marks
- Mixing feet of head with psi without the 2.31 conversion.
- Treating a chlorine residual reading as valid without noting whether it is free or total chlorine.
- Sampling at convenient sites that are not approved distribution locations.
- Returning a repaired main to service before satisfactory bacteriological results.