What is Water Pollution?

Contamination of water bodies because of the discharge of pollutants into them is known as water pollution.

Sources of Water Pollution

Natural Sources

  • Gases, minerals, humus and wastes created by living organisms are some natural wastes which pollute water.
  • Minerals such as nickel, sodium, lead and mercury also pollute water.

Man-made Sources

  • Household detergents and wastes pollute water bodies. Water that is drained out after its use in various households is called wastewater. When this wastewater mixes with solid wastes such as plastics, animal dung, and human faecal material, it is known as municipal wastes.
  • When detergents and fertilizers containing phosphates are discharged into water, it promotes the growth of algae. This is known as eutrophication. Aquatic wastes interfere with fishing, navigation, and irrigation.
  • Industrial wastes include heavy metals and synthetic organic compounds. Discharge of these wastes into water bodies causes water pollution. Lead, manganese, and mercury affect marine life.

Off-shore Drilling and Oil Spills

  • Drilling of oil under the sea may prove dangerous for marine life.
  • Oil is transported to distant places by ships. An oil spill or tragedy at sea wherein the ship capsizes causes degradation of marine and aquatic organisms. It also threatens ecosystems which exist under the sea.
  • Oil may also spill into the sea as a result of offshore drilling.

Types of Water Pollutants

According to the World Health Organization, any foreign matter either natural or other sources which contaminate and pollute the water or the water supply making it harmful for human and aquatic life is termed water pollution. Various types of water pollutants are

  • Biological pollutants: Viruses, protozoa, fungus, bacteria, algae
  • Organic chemical agents: Gasoline, pesticides, insecticides, oil
  • Inorganic chemical agents: Acids, nitrates, phosphates, salts
  • Physical pollutants: Suspended solid particles, heat

Effects of Water Pollution

Water pollution may severely affect human, plant, and animal life. The effect of water pollution on marine animals and plants is visible in two phenomena—eutrophication and biomagnification.


It is a process in which oxygen begins to deplete from water bodies either naturally or because of human activities. Nutrients and chemicals are discharged into water bodies through sewage and effluents. Accumulation of these into water bodies results in the growth of phytoplankton and algae. This obstructs the penetration of oxygen and sunlight into water bodies which may result in the death of aquatic organisms.


When the quantities of harmful substances such as pesticides and insecticides increase in the food chain of marine and aquatic organisms and are in turn consumed by other living beings, it is known as biomagnification.

Effects of Water Pollution on Human Health

  • Pathogens are disease-causing bacteria present in wastewater. When contaminated water is consumed, the pathogens enter the human body. It may cause various water-borne diseases such as typhoid, cholera, diarrhoea, dysentery, and jaundice.
  • Metals such as lead, mercury, and cadmium dissolved in water may cause several diseases if they enter the human body. When water contaminated with cadmium was consumed by the Japanese, they were affected by a disease called itai-itai. Similarly, a disease known as Minamata affected the Japanese after they consumed fish that had a large concentration of mercury.

Other Effects of Water Pollution

  • When phosphorus and nitrates from fertilizers are disposed of in water bodies, they promote the growth of algae. The presence of algae in water bodies in a large number reduces the amount of dissolved oxygen in water resulting in the death of fish and other water organisms.
  • Industrial effluents include chemicals such as mercury, lead, and cadmium. When these chemicals reach the human body through the consumption of fish, they may cause irritation, insomnia, and nervous disorders, which may also affect the brain.
  • Thermal pollution increases the temperature of the water which in turn reduces the level of oxygen in the water. This results in the death of many species of fish. Oil drilling and oil spills contaminate seawater which may also lead to the death of marine organisms.

Prevention of Water Pollution

Non-Point Sources

Sources of water pollution which cause an inflow of pollutants over a large area are known as non-point sources. Example: Runoff from agricultural fields. The following steps should be taken to reduce water pollution from non-point sources:

  • Two separate drainages should be built for sewage and rainwater so that both rainwater and sewage do not overflow together.
  • Nitrogen-fixing plants should be planted to reduce the use of chemical fertilisers.
  • Agrochemicals and pesticides should be used judiciously to prevent them from draining into a water body.
  • Efforts should be made to prevent runoff of manures.
  • Biofertilisers and biopesticides should be used.

Point Sources

Sources that discharge pollutants to only one specific site are known as point sources. Example: Discharge of effluents from the factory into a river. To prevent pollution from point sources, it is essential to first treat wastewater before it is discharged. Laws should be made carrying strict punishment for discharging untreated wastewater into any water body.

Treatment of Plants

Wastewater should undergo three types of treatments to purify it. These are

Primary Treatment

  • In primary treatment of water, screens, grit chambers and sedimentation tanks are arranged in a serial order.
  • Water which passes through them is treated with chlorine gas which kills the harmful bacteria in water. However, dissolved organic matter like salts cannot be treated in this method.

Secondary Treatment

  • In this method, the organic matter which is present in water is biologically degraded by microorganisms. When water enters a tank, it comes into contact with microorganisms.
  • Air is introduced into the tank through diffusers. Microorganisms in the presence of oxygen break the organic matter and the impurities then settle to the bottom of the tank which is later removed.
  • Water is then treated with chlorine gas which then kills the rest of the harmful organisms.

Tertiary Treatment

In this method, nutrients such as nitrogen or phosphorus are removed. This water can be reused for industrial, agricultural, and domestic purposes.

Also, Read What is Air Pollution?