21 September 2014

Water Pollution : Science

Water Pollution : Science NCERT / CBSE Revision Notes

Life on earth would be quite impossible without water. Water covers two-thirds of the earth’s surface and makes up 75 per cent of the human body.

A water body is said to be polluted when toxic substances damage it, making it undrinkable and also dangerous for organisms to live in it. Harmful substances like sewage, silt, toxic - chemicals and domestic waste are called water pollutants. They spoil the quality of water by altering its smell and colour and render it unfit for drinking.

Water Pollution : Science, Prevention of Pollution, CBSE / NCERT Revision Notes

Pollution can enter a body of water in many ways such as domestic sewage, agricultural run-off containing fertilisers and pesticides, eroded soil, acid rain, chemicals released from industries or other wastes from cities and towns.

Must Read:  Air Pollution

Domestic sewage is waste water from our homes. It contains many dissolved and suspended impurities. People dump their garbage into streams, lakes, rivers and seas, thus polluting the water with cans, bottles plastics and household waste. Fertilisers contain chemicals that dissolve in water. Hence, agricultural or irrigation run-off has a high nitrate content due to the use of fertilisers and pesticides. As the water seeps into the ground, it greatly affects the groundwater quality, thereby polluting it. Wastewater released from manufacturing or chemical processes in industries also contribute to water pollution.

At places along the Ganga, people bathe, wash clothes and even defecate in the water. They also throw huge quantities of garbage, flowers, idols of gods and goddesses, untreated sewage, animal carcases and non-biodegradable polythene bags directly into the river. Industries along the Ganga, such as oil refineries, paper factories, and textile and sugar mills, discharge their toxic chemical wastes into the river.

Chemical contamination of water due to chemicals, such as compounds of arsenic, fluorides and lead, cause plants and animals to die. The soil is also affected by polluted water, causing changes in its acidity, and, therefore, the growth of plant life. Polluted water is unsuitable for drinking, recreation, agriculture and industry.

Contaminated water destroys aquatic life and reduces its reproductive ability. Water pollution drastically reduces the quantity of dissolved oxygen in water, which results in the death of aquatic organisms. Anaerobic micro-organisms release gases like methane and hydrogen sulphide, leaving a foul-smelling, waste-filled body of water.

The large quantities of chemicals that are washed in from the fields are responsible for the excessive growth of algae. Once the algae die, it serves as a food for bacteria. As a result, a lot of oxygen in the water is used up and many aquatic organisms die.

Potable water

Water that is suitable for drinking is called potable water. Sewage treatment plants treat wastewater to purify it before releasing it back into rivers and lakes. Municipal bodies treat water before supplying it to our households.

Some popular ways of making water potable are:

  • Using candle type water filters
  • Boiling
  • Chlorination

Reduce, reuse and recycle is a popular mantra and one that is so important for us to practise.

Steps to conserve water:

  • Rain water harvesting 
  • Using drip irrigation method in agriculture
  • Reusing the water used to wash vegetables
  • Minimising water consumption