DAV Class 8 Science Chapter 20 Notes – Pollution of Water

These DAV Class 8 Science Notes and DAV Class 8 Science Chapter 20 Notes – Pollution of Water act as excellent revision resources, particularly in preparation for board exams.

Pollution of Water Class 8 DAV Notes

→ Water Pollution: The change in normal properties of water by the presence of foreign materials is called water pollution.

→ Water Pollutants: The substances (foreign materials) which pollute water are called water pollutants.

→ Signs of Water Pollution:

  • Bad taste of drinking water.
  • Offensive odour from lakes, rivers, and ocean beaches.
  • Unchecked growth of aquatic weeds in waterbodies.
  • Decrease in number of fish in fresh water, river water, sea water, etc.
  • Oil and grease floating on water surface.

DAV Class 8 Science Chapter 20 Notes - Pollution of Water

→ Causes of Water Pollution:

  • Human activities like bathing and washing of clothes in rivers and ponds.
  • Industrial wastes also pollute water to a large extent and are responsible for many diseases.
  • Agricultural wastes like fertilisers, pesticides also pollute groundwater. When this polluted water is consumed, these chemicals enter the body of aquatic animals and other animals.
  • Domestic sewage is often released into rivers. The sewage promotes the growth of algae and bacteria which use up a large amount of oxygen dissolved in water. This causes depletion of oxygen in water. This leads to death of aquatic animals.
  • Oil spills from tankers in high seas.
  • Pollution of water by acids is harmful to aquatic life.

→ Potable Water: Water which is fit for drinking is called potable water. Potable water should meet following criteria:

  • It must be colourless and odourless.
  • It must be free from suspended impurities.
  • It should be tasteless.
  • It must be free from microorganisms which lead to many diseases.
  • It must be free from harmful chemicals.

→ Purification of Drinking Water:
In households, water is filtered by a candle filter or electric filter. Purification of water removes suspended impurities and destroys harmful germs.

→ Methods to obtain safe drinking water:

→ Filtration: Water can be purified by passing it through sand, gravel and charcoal. This is a physical method of removing impurities.

→ Boiling: Boiling usually kills most of the germs in water.

→ Chlorination: Chlorine powder or tablets are added to water which kills the germs in water.

→ The amount of chlorine tablet should not be more than what is specified, otherwise it can turn poisonous.

→ Control of Water Pollution:
Industrial wastes and sewage are the two major sources of water pollution. Treatment of sewage can be done by using following methods:

  • Sewage is churned by machines and then is passed into a tank with a gentle slope. Heavier particles settle down and the water flowing down is relatively pure.
  • Treatment of water with alum also helps in its purification.
  • Water is then sterilized by chlorination.
  • The chemical substances present in the industrial waste can be precipitated by suitable chemicals and removed from water.
  • Water treatment plants should be installed in all industrial areas.

→ Conservation of Water:

  • Avoid using shower and use a bucket and mug for bath.
  • Do not leave the tap open while brushing your teeth.
  • Use water left after washing clothes for watering the plants.
  • While washing your hand, do not leave water running for rinsing.

DAV Class 8 Science Chapter 20 Notes - Pollution of Water

→ Water Pollution :Addition of contaminants in water is called water pollution.

→ Sewage :Wastewater coming from households is called sewage.

→ Effluents :Wastewater coming from factories is called effluent.

→ Chlorination :Treatment of water by chlorine.

→ RO filter :A water filter which works on Reverse Osmosis.