Water Supply and Drainage
This domain tests potable water supply - demand, storage, boosting, distribution pressure, hot water and the drainage of the supply side - as regulated by Mabhas 14 and Mabhas 16.
Demand, storage and pressure
Estimate demand from occupancy: residential consumption commonly taken in the 150–250 L per person per day range, offices far lower, plus a fire reserve kept separate. Storage is usually sized for one to two days of demand plus fire volume, in a tank with access, overflow and a vent. Pressure at fixtures must be adequate (about 1.5 bar minimum) and limited (about 4–5 bar maximum), so tall buildings are zoned, commonly one pressure zone per 30–35 m of height, with pressure-reducing valves. Keep riser velocities around 1.5–2 m/s to avoid noise and erosion. Hot water is stored near 55–60 °C with a return line and thermostatic mixing at outlets; dead legs breed Legionella.
Worked example
A booster serves 5 L/s with 30 m static lift to the top fixture, 10 m friction loss and 15 m residual pressure required. Total head = 30 + 10 + 15 = 55 m. Shaft power = ρgQH/η = (1000 × 9.81 × 0.005 × 55) / 0.70 = 3.85 kW, so select a 5.5 kW motor. Note the static term counts upward only; the down-leg does not add head, though it adds friction.
Traps
Adding up-feed and down-feed static heads together; forgetting residual pressure at the highest fixture; sizing risers on flow alone without a velocity check; no expansion vessel or non-return valve on the cold feed to the heater; ignoring backflow protection at boiler filling and irrigation connections; and no provision for draining and disinfecting the tank.