Water Supply Systems: Pipes, Fittings and Installation
What this domain tests
Water supply questions cover layout, pipe materials, jointing, valves and testing. Expect direct versus indirect supply, upfeed and downfeed, sizing, and pressure testing before concealment.
Core rules and concepts
- Direct supply feeds from the mains; indirect supply fills a storage tank first. Indirect supply gives steadier pressure and storage during cuts.
- Upfeed: a pump lifts water to an overhead tank. Downfeed: gravity carries water from the tank to fixtures.
- Common materials: GI, copper, PVC-U, CPVC, PPR and HDPE. Match the joint method to the material.
- Joints: threaded for GI, soldered or pressed for copper, solvent-cemented for PVC/CPVC, heat-fused for PPR and HDPE.
- Fit isolation valves and unions so sections can be isolated for repair.
- Test newly installed pipework before concealment, commonly at 1.5 times the working pressure, and check for leakage.
- Provide air release at high points and drain valves at low points.
Worked example
A hostel has 5 residents at 135 litres per person per day. Daily demand = 5 × 135 = 675 litres. If one day of storage is required, choose a 1000-litre overhead tank. The reasoning: storage must exceed demand to cover variation and refill time; the next standard size above 675 litres is 1000 litres. Check that the tank outlet, overflow and cleaning access are correctly sized.
Traps that cost marks
- Applying solvent cement to a threaded joint.
- Burying pipework before pressure testing.
- Omitting a union or isolation valve at a pump or tank outlet.
- Using a smaller supply pipe than the fixture demand requires.
- Forgetting that hot-water pipe expands and needs room to move.