Water Supply, Storage and Distribution
This domain tests how water gets from the main to the outlet at the right pressure, flow and quality, and how stored water must be protected.
Service and supply
The communication pipe belongs to the water utility up to the boundary or stopcock; the supply pipe from there to the building is the customer's. Design pipe sizes using loading units to EN 806 / BS 8558 rather than guessing from the number of outlets.
Storage
A typical dwelling is designed around 200–230 L of stored cold water, with a 24-hour reserve. The tank needs a close-fitting lid, a screened warning pipe, a screened vent, insulation and a rigid base, and should not sit directly above electrical equipment. Where backflow risk demands it, use a Type AB air gap or equivalent.
Direct and indirect systems
- Direct: all outlets fed from the mains; simple, good pressure, but no reserve.
- Indirect: tank feeds cold and the cylinder, giving a reserve and lower outlet pressure. Boost with a pump set or accumulator where the mains is marginal.
Worked example
A combi boiler in a rural house keeps tripping out on low pressure. Measure: static 2.8 bar but dynamic only 0.9 bar at 8 L/min - the mains cannot sustain the boiler's minimum. Options: an accumulator, a break tank and booster set, or a stored system. The reasoning matters: static pressure is not the test, dynamic pressure and flow together are.
Traps that cost marks
Sizing from outlet count; forgetting a 24-hour reserve; putting a tank where it cannot be inspected; assuming a high static reading proves adequate flow.