Water Supply Systems, Storage and Distribution
What is tested
This domain covers source-to-tap arrangements: direct municipal supply, indirect supply through an underground sump and overhead tank, pumping, storage, distribution pipework and pressure. Expect questions on air gaps, backflow, valve placement, pipe sizing and tank maintenance.
Core rules
- Prefer indirect supply where municipal pressure is intermittent; keep an air gap between the inlet and the tank's maximum water level.
- A sump should be covered, raised above the floor, and separated from drains; clean and disinfect it on a schedule.
- Pump suction should be short and free of air traps; fit a foot valve or non-return valve as required.
- Overhead tank outlet should be slightly above the tank bottom to avoid drawing sediment; fit a washout and overflow with insect screen.
- Distribution should use a manifold or balanced branches; avoid long dead legs where water can stagnate.
- Pressure from an overhead tank is about 0.1 bar per metre of head, less friction loss. A 12 m head gives roughly 1.2 bar static.
Worked example
A tap is 12 m below the tank water level. Static pressure is about 12 × 0.1 = 1.2 bar. If the pipe run has 0.3 bar friction loss at design flow, the tap sees about 0.9 bar. If the fixture needs 1.0 bar, increase pipe size, shorten the run, or raise the tank; a booster pump is the last resort.
Traps
Do not connect a municipal line directly to a private tank without backflow protection. Do not size a pump from tank capacity alone; use flow and head. Do not leave the tank uncovered. Do not ignore a leaking float valve, which wastes water and overflows the tank.