Pollution of Water- Biology Guide for Class 8

Pollution of Water- Class 8 Science Guide

Information about Water Pollution


Pollution of Water


Class 8


Class 8 Biology

Topics Covered

  • Water Pollution
  • Causes of Water Pollution
  • Potable Water
  • Purification of Drinking Water
  • Methods that can be used to Make Water Safe for Drinking Purposes
  • Treatment of Major Sources of Water Pollution
  • Conservation of Water

We learnt that water is a precious resource. We also learnt about the scarcity of water and its causes. Some of these causes are: increasing population, increase in industries, agricultural needs, poor rainfall and deforestation. Next to air, water is most essential for all living beings - the plants, animals as well as the humans. Water covers nearly three-fourth of earth's surface, it does so in the form of snow over mountains and as liquid water in oceans, lakes, rivers and ponds. The quality of water is of prime concern when it has to be used for drinking by humans as well as by animals.

Water Pollution

Water has the property to dissolve a large number of substances. This property of water often becomes a major cause of its pollution; the 'dissolved substances' may be harmful for plants and animals.
  • Water pollution is defined as the change in the normal properties of water due to the presence of foreign materials.
  • The substances (foreign materials) that pollute water are called water pollutants.
The presence of pollutants in water can be recognised through one or more of the following 'changes' in the normal properties of water. 
  1. Bad taste of drinking water.
  2. Offensive odour from lakes, rivers and ocean beaches.
  3. Unchecked growth of aquatic weeds in water bodies.
  4. Decrease in number of fish in fresh water, river water or sea water.
  5. Oil and grease floating on water surface.

Causes of Water Pollution

Water pollution can be caused in a number of ways. Some of these are mentioned below:

  1. Human activities, like bathing and washing of clothes, in rivers and ponds, can pollute the water in them.
  2. Industrial wastes also pollute water to a large extent; they are responsible for many water borne diseases. 
  3. Agricultural wastes, like fertilisers and pesticides, also pollute the underground water. When this water is used for drinking, it harms the human body. The fertilisers and pesticides also enter different water bodies, where the chemicals (present in them) harm both aquatic animals and plants.
  4. The domestic sewage of cities is often released into rivers. This sewage promotes the growth of algae and bacteria which use up a large amount of oxygen dissolved in water. This can cause a depletion of oxygen in water which can lead to death of aquatic animals.
  5. Oil spills, from oil tankers transporting crude oil, often pollute the oceans causing damage to marine life.
  6. Pollution of water by acids is harmful to 'aquatic life'. We have already discussed about 'acid rain' in the previous chapter. When rain water, containing high proportion of such acids, mixes with sea water, it pollutes it.

Potable Water

Very often, when we go out, we prefer to carry our water bottle along with us. Let us understand what kind of water is fit for drinking.
  • Water, which is safe for drinking, is called potable water.
Potable water does not cause any water-borne disease (like jaundice, diarrhoea, etc.) 

The following parameters need to be followed before water is supplied for drinking purposes:
  1. It must be colourless and free from any odour or smell.
  2. It must be free from suspended impurities.
  3. It should be tasteless.
  4. It must be free from microorganisms which lead to many diseases.
  5. It must be free from harmful chemicals. 

Purification of Drinking Water

Keeping in view the importance of pure drinking water, we must ensure that the water we drink, is free from impurities and germs.
It is clear, therefore, that the purpose of purification of water, is to-
  1. remove suspended impurities.
  2. destroy harmful germs.

Methods that can be used to Make Water Safe for Drinking Purposes

1. Filteration

Water can be purified by passing it through layers of sand, gravel and charcoal, one by one. This is a physical method of removing impurities. This has been, and can still be, the method that may be used in the absence of alternative and more advanced methods.

2. Boiling

Boiling is quite a good method to purify water; the high temperature, attained during boiling, kills germs.

3. Chlorination

This is a chemical method for purifying water. It is done by adding chlorine tablets (or bleaching powder) to water. This is a method that needs to be used with care. We should not use more chlorine tablets than specified.

4. Loading

Suspended particles are made heavier through their accumulation around alum. The resulting heavier particles then tend to settle down; clean water can then be decanted off.

Treatment of Major Sources of Water Pollution

Two major sources of pollution are:
  1. Sewage
  2. Industrial wastes
They should be removed from water before it is put to use.

Treatment of Sewage

Following measures must be taken to check pollution by sewage:
  1. Sewage must be churned by machines. The churned sewage is passed into a tank with a gentle slope. Heavier particles settle down and the water, flowing down, is relatively pure. 
  2. Treatment of water with alum also helps in its purification. 
  3. Water must be sterilised by chlorination. It kills the microbes. 

Treatment of Industrial Waste

The treatment of industrial waste depends upon the nature of the pollutants present. Chemical substances, present in the industrial waste, that get dissolved in water, can be precipitated by suitable chemicals; they can then be removed from water.

Laws for industrial units need to be strictly implemented and enforced. Polluted water must not be disposed off directly into rivers and lakes. Water treatment plants should be installed in all industrial units.

Conservation of Water

Some suggestions by which we can save water:
  1. Avoid using shower; it is better to use a bucket and mug for taking bath.
  2. Do not leave the tap open while brushing your teeth. 
  3. Never let water go down the drain when there may be another use, such as watering a plant, or cleaning for it.
  4. Do not leave the water 'running' when washing dishes by hand.
  5. Do not wash your car with tap water using a pipe.
At the individual level, we should consciously try to save water and not waste it. The principle of 3R's - Reduce, Reuse and Recycle - should be our guiding principle. 

Previous Post Next Post