Water Supply and Distribution: Pressure, Sizing, and Protection
Supply system basics
Water supply systems deliver potable water at adequate pressure and volume. The system includes the service line, meter, main, risers, branches, and fixtures. Sizing depends on fixture units, demand, developed length, and pressure loss. Candidates should understand that pressure drops with elevation and friction, and that the minimum residual pressure at the most remote fixture governs design.
Materials and installation
Supply pipe materials must be approved for potable water. Joints must be made with approved methods. Pipes must be supported, protected from freezing, and separated from drainage piping where required. Backflow protection is required at cross-connections, and thermal expansion must be accommodated.
Hot water
Hot water systems must deliver water at safe temperatures. Tempering valves are required at fixtures accessible to children, the elderly, or persons with disabilities. Recirculation may be required to maintain temperature.
Traps in questions
Watch for undersized supply lines, missing backflow protection, and improper separation of water and waste piping. Also watch for questions about pressure at the top floor.
Worked example
A three-story building has adequate street pressure at the main but low pressure at the top floor. The designer must account for static pressure loss of about 0.433 psi per foot of elevation, plus friction loss, and may need a booster system.
Rule of thumb
Size supply lines for the most remote fixture at the minimum residual pressure, and never assume street pressure is enough on upper floors.