Water Supply Systems and Pipe Layout
Scope
This domain tests direct and indirect supply, overhead tanks, downfeed and distribution layouts, pipe sizing, valves, pressure and testing. The exam expects you to lay out a system that delivers adequate pressure without contamination.
Core rules
- Estimate demand from fixture units and occupancy; size mains and branches within design velocity, commonly about 1–2 m/s.
- Keep a minimum residual pressure at fixtures; flush valves commonly need about 0.5 bar.
- Provide a gate or ball valve at the tank outlet and at each branch, plus a drain valve at the low point.
- Avoid dead legs, trapped air and cross-connections; protect potable lines from backflow.
- Support pipes at specified spacing and allow expansion in hot-water lines.
- Pressure-test before concealment, commonly at 1.5 times working pressure or as specified.
Worked example
A tank feeds a bathroom 8 m below its water level. A 10 m water column gives about 0.98 bar, so 8 m gives about 0.78 bar before friction loss. If the fixture needs 0.5 bar, the available margin is about 0.28 bar. Check the pipe size and length; if friction loss exceeds 0.28 bar, raise the tank or enlarge the pipe. Reason: static head minus friction loss must exceed the fixture requirement.
Traps
Sizing by guesswork; ignoring friction loss; placing the tank too low; no isolation valves; connecting a pump directly to the public main without approval.