3.12 THE TECHNOLOGY OF WATER SUPPLY

The water we use in our homes comes from lakes, rivers or wells, or sometimes from rain that we collect. In the past, water had to be collected in buckets, and this still happens in many regions. But now, more and more of us obtain water simply by turning on a tap. Three important parts of a modern water supply system are reservoirs, pipes, and taps.

Reservoirs are places where water is stored before it goes to homes and factories. Reservoirs must be situated above the places they supply. The pressure of the water coming out of a tap depends on the height of the water level above the tap. Reservoirs may be natural lakes, or lakes created by damming rivers, or large water tanks. Dams need to be very strong to hold back the huge mass of water in the lakes behind them. A dam must be thicker at the bottom than the top because the water pressure increases with depth. Water tanks are often used as reservoirs around villages and towns. They may be filled from larger reservoirs in the hills or by pumping underground water from wells or bore holes. They must be situated on high ground nearby or on specially built towers. The towers have to be very strong because water is so heavy.

A cross section through a dam

Pipes carry water from one place to another. The pipes that carry water from local reservoirs to peoples' homes are usually made of galvanised iron or black plastic. Galvanised iron is covered with a layer of zinc metal to stop it from rusting. T-joints are needed to connect branches that go off at right angles. L-joints are needed for sharp bends, especially in galvanised iron pipes, which are not very flexible. The pipes are screwed into the joints. Wider plastic pipes are used for drains to carry away waste water. Drainpipes need T-joints and L-joints too, but they are often glued, not screwed.

Taps control the flow of water from the end of a pipe. The water flows through a hole surrounded by a flat valve seat. When the tap is closed, a rubber washer on a valve disk seals the hole and the water cannot flow. The tap is opened by turning the handle anti-clockwise. This raises the valve disk and the washer and allows the water to flow. Turning the handle clockwise, screws the valve disk down onto the valve seat, and the washer seals the hole again. Taps should be closed gently. Screwing down too hard soon destroys the rubber washer and may damage the valve seat. When a tap leaks it probably needs a new washer. It is easy to take a tap apart with a spanner, and replace the washer - but don't forget to stop the flow of water to the tap first! If the valve seat has been damaged, a new tap may be needed.

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  • 1. What does the water pressure in a tap depend on?
  • 2. Why are local water tanks often placed on high towers?
  • 3. What is a T-joint and how are pipes fixed to it?
  • 4. How would you try to fix a tap that starts dripping?

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