Treatment of Water

In cities, drinking water is supplied from water works. In water works, the methods like sedimentation, decantation, loading, filtration and chlorination etc. are used to remove undesirable materials from water. The source of water supply in a city is either a nearby river or a lake called a reservoir. The river water and lake water usually contain suspended solid substances and some germs, so, before this water can be supplied to homes, it must be purified to remove suspended impurities as well as germs. 

Water purification system in water works

The purification of river water or lake water is done in the following steps.

1.0Sedimentation

The water is allowed to stand in big tanks, where heavier suspended impurities settle down. To increase the rate of sedimentation, alum is added to it. The impurities settle at the bottom.

2.0Filtration

The semi-clear water is allowed to pass through beds of sand, charcoal and gravel to remove suspended impurities.

3.0Removal of Harmful Organisms or Sterilisation

The harmful bacteria in filtered water can cause very serious diseases such as typhoid, cholera, etc. Thus, to the filtered water, bleaching powder or chlorine gas is added. This kills the micro-organisms and hence the water becomes fit for drinking. This water is directly pumped into overhead tanks for supply to a city.

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