Water Supply and Distribution Systems
Water Supply and Distribution Systems tests pipe sizing, pressure, flow, backflow protection, thermal expansion, and water-heater safety. Expect calculations using static pressure, elevation, and friction loss, plus questions on cross-connection control.
Core rules
- Size water piping by fixture units, developed length, and available pressure. A long run or high fixture load requires a larger pipe.
- Static pressure above 80 psi requires a pressure-reducing valve. A closed system needs a thermal expansion tank at the water heater.
- Backflow protection is required at cross-connections. An air gap is the strongest protection; vacuum breakers and testable reduced-pressure assemblies are used where the code permits.
- Water-heater temperature-and-pressure relief valves are set to open at 210°F or 150 psi, whichever occurs first, and must not be capped or plugged.
- Potable water pipe and fittings must be lead-free.
Worked example
A meter supplies 60 psi static pressure. A fixture is 10 feet above the meter, and piping friction loss is 12 psi. Elevation loss = 10 x 0.433 = 4.33 psi. Available pressure = 60 - 4.33 - 12 = 43.7 psi. That is adequate for most fixtures but may be marginal for a flushometer valve, which needs a higher residual pressure. The reasoning: subtract elevation and friction from static pressure before comparing to the fixture minimum.
Traps that cost marks
- Using static pressure without subtracting elevation and friction loss.
- Omitting a pressure-reducing valve above 80 psi.
- Installing a check valve or backflow preventer without providing thermal expansion control.
- Treating a hose-bib vacuum breaker as equivalent to an air gap.
- Capping or plugging a T&P relief valve.