24 December 2011

8th Pollution Of Air And Water (CBSE Science)


Water pollution: The contamination of water that changes in the physical, chemical and biological conditions of water is called water pollution. This makes water unfit for human consumption.
Whenever harmful substances such  as sewage, toxic chemicals, silt, etc., get  mixed with water, the water becomes  polluted. 
The substances that pollute  water are called water pollutants.
1.Many industries discharge harmful chemicals into rivers and streams, causing the pollution of water.
2.Use of pesticides and weedicides . These chemicals dissolve in water and are washed into water bodies from the fields. They also seep into the ground to pollute ground water.
3. The bacteria present in the faeces of mammals.
4. Throwing  untreated sewage directly into rivers.
Water which is suitable for drinking is called potable water.
water can be made 
safe for drinking:
1. By filtering water. A popular household filter is a candle type filter.
2. By boiling Water.Boiling kills the germs present in the water
3. Chlorination is a commonly used chemical method for purifying water.It is done by adding chlorine tablets or bleaching powder to the water
WHAT YOU HAVE LEARNT
  1. Water pollution is the contamination of water by substances harmful to life.
  2. Sewage, agricultural chemicals and industrial waste are some of the major contaminants of water.
  3. Water which is purified and fit for drinking is known as potable water.
  4. Water is a precious natural resource. We must learn to conserve it.

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