Water Supply Systems and Domestic Plumbing Layout
System types
- Direct (mains-fed): supply taken straight from the municipal main; cheap, but pressure is unreliable and backflow is a risk when the main runs intermittently.
- Indirect (tank-fed): main → underground sump → pump → overhead tank (OHT) → gravity distribution. This is the standard domestic layout in Punjab and the one most exam sketches ask for.
- Combination: indirect storage with a direct connection for the ground-floor kitchen tap.
Components in flow order
Ferrule → water meter → main stop cock → sump inlet with float valve and overflow (the overflow must discharge visibly, never secretly into a drain) → suction line with foot valve and strainer → monoblock or submersible pump → non-return valve → OHT with float valve, overflow and air vent → downtake → distribution branches → gate or ball valve on each riser → fixtures.
Sizing and pressure
IS 1172 suggests about 135 litres per capita per day for domestic use, so a five-member household needs roughly 675 L/day and a 1000 L OHT gives one day's storage with margin. Size the downtake generously (25–32 mm) so top-floor fixtures still receive 1–2 m head. Keep velocities moderate (about 1–2 m/s) to avoid noise and water hammer; fit a non-return valve and, on long vertical runs, an air chamber.
Worked example. A 5-person house with one bathroom and a kitchen. Demand = 5 × 135 = 675 L, so select a 1000 L OHT. With only one bathroom drawing at a time, a 25 mm downtake is adequate; specify 32 mm if two bathrooms may draw together. Reasoning: demand gives the tank size; simultaneous draw, not the number of taps, gives the pipe size.
Traps that cost marks
No air vent on the tank (it bulges or collapses); an overflow piped secretly into the SWR line; undersized downtake causing weak top-floor flow; no non-return valve, so the pump cycles.