Water pollution: Spoiling the quality of water by any natural or human activity is called water pollution. 

Causes of water pollution: 

1. Waste products, industrial wastes and chemical wastes are thrown in rivers, lakes, etc. as such pollute the water bodies. 

2. Sewerage and dirty waste water of villages, towns and cities is drained to fall into rivers or any other water body. 

3. People wash their dirty clothes, take bath, clean their utensils and bath their pet animals in the water of the pond, lake, river, etc. 

4. Oil slick in the sea due to leakage, from ship, causes pollution. Water is also polluted, due to atomic explosions in seas. 

5. Atomic explosion experiments inside the sea, and dumping of nuclear waste in oceans.

Harmful effects of polluted water on human life:

1. Water plants and animals are destroyed, due to polluted water by industrial wastes. 

2. Sewerage, garbage and organic materials dumped into water bodies, kill the fishes, because of reduction in oxygen concentration, causing their suffocation. 

3. Many diseases are caused by drinking polluted water, e.g., typhoid, cholera, dysentery, jaundice, hepatitis and polio. 

4. Eggs of hookworms, roundworms, etc. enter into our bodies through polluted water and make us ill. 

5. Parasites penetrate the skin of human beings while bathing in polluted water, it becomes the cause of diseases such as schestomiosis, laptospisosis, etc. 

6. Water discharged from some industries may contain metals like copper, chromium, zinc, cadmium. These metals are harmful to human beings and cause diseases. 

For example, Minamata disease is caused due to mercury metal. This disease harms the liver and kidneys. 

7. Fluorine ions present in water causes fluorosis of teeth and bones, Problems of kidney and thyroid gland are produced, due to the high concentration of fluorine.