Domestic Water Supply
Domestic water in a building is the fresh water supplied to washrooms, showers, urinals, toilet bowls, kitchen, garden and other places. The water is for general purpose washing, sanitary, drinking, and cooking.
Water from the Water Supply Board is first piped into a storage tank for the building. This storage tank is normally situated at the ground floor level or lower. From this tank, the water is pumped to a header tank situated at the roof top of the building.
With the help of level float valves installed at the inlet pipe to the tanks, the water level in the tank can be controlled. The level float valves shut off the water mechanically when the level becomes high. Electrical level controls installed at the tank top is used to start and stop the pumps.
From this header tank, water is taken out through pipes and distributed to the user points.
The water pressure at the user points is proportional to the height of the rooftop tank from it. Some buildings that are low can make use of tanks constructed on top of steel or concrete structures. The higher the tower structure, the higher the pressure will be.
Some systems do not use header tanks at the roof top. They achieve their pressure by the use of hydrostatic tanks. These are pressure vessels containing air. Pressure switch installed on the tank senses any pressure drop in the tank. When some user further down the line opens a tap, the pressure in the tank drops. When the pressure reaches to a set value, the pressure switch activates a signal to start a pump.
The pump starts to transfer water from the storage tank to the hydrostatic tank and pressurize it. The pressure builds up in the tank, and the air above the water gets compressed. At a set cut-out pressure, the pump stops. The pressure of the air is sufficient to force the water to the user point.
The hydrostatic tank is usually lined with rubber. The tank serves like a buffer to even up any pressure fluctuation in the distribution system. This is because whenever a pump starts, the pressure builts up very fast. With the hydrostatic tank in use, the pressure is felt by the tank, and is not transmitted to the user point.
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