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Water Pollution

Release of pollutants such as sewage, pesticides, herbicides, factory wastewater, etc., into natural water bodies causes water pollution. In this concept, the students will understand effects of water pollution.

After reading the concept, students will be able to:

  • Discuss what is water pollution.
  • Compare different causes of water pollution.
  • Describe how destruction of ecosystem and eutrophication causes water pollution.
  • Compare different methods for prevention of water pollution.
  • Recall the working of water treatment plant.

Each concept is explained to class 4 students using descriptions, illustrations, and concept maps. After you go through a concept, assess your learning by solving the two printable worksheets given at the end of the page.

Download the worksheets and check your answers with the worksheet solutions for the concept Water Pollution provided in PDF format.


What is Water Pollution?

Water pollution occurs when unwanted substances are released into the water bodies that make the water unsuitable for human use and cause harm to the aquatic plants and animals. Human activities usually cause this type of pollution.

What is water pollution for kids


Water pollutants :

Some of the common water pollutants are—

Sewage: It is one of the most common water pollutants as even now sewage is released directly into streams and rivers in many areas. As a result, the water gets contaminated with harmful bacteria that cause illness among human beings and animals.
 Sewage and other water pollutants
Pesticides and herbicides: Pesticides are chemicals sprayed on crops to kill pests, whereas herbicides are sprayed to control unwanted vegetation. These strong chemicals can seep into nearby waterbodies from the agricultural fields, making the water toxic.
Agriculture water pollution
Wastewater Released by Factories: Factories use large quantities of water to process chemicals, keep the machines cool, and for cleaning purposes. Sometimes, the wastewater from the factories is directly released into rivers or the ocean. As the wastewater contains chemicals and other pollutants, it degrades the overall water quality.
Indusrial wastewater sources



Causes of Water Pollution:

  • Human activities like bathing, washing clothes and utensils and bathing domestic animals in ponds, lakes and rivers.
  • Discharge of sewage into the waterbodies.
  • Chemicals released into the waterbodies from agricultural run-off.
Causes of water pollution in points
  • Accidental oil spills from oil tankers cause water pollution. The oil spreads out rapidly across the water surface and forms a layer called an oil slick. It prevents oxygen from dissolving in the water, and aquatic organisms die due to oxygen deficiency. Example: Oil spill in the Gulf of Mexico (also called the Deepwater Horizon oil spill) in 2010.
  • Discharge of wastewater and hot water released from industrial plants.
Oil spillage in sea


Effects of Water Pollution:

  • Diseases : Drinking or consuming polluted water causes different diseases like typhoid, cholera, hepatitis and other diseases.
  • Destruction of Ecosystems: Ecosystems respond to even small changes in the environment. Thus, water pollution can cause a total ecosystem to collapse if left unmonitored.
Eutrophication : A waterbody becomes enriched with nutrients when there are excess chemicals in the water. This phenomenon is called eutrophication. Such a nutrient-rich environment causes rapid growth of algae (also known as algal bloom) that forms a top algal layer on the waterbody. These algae utilize the oxygen dissolved in water and block sunlight from entering the deeper layers of water. As a result, aquatic life gets severely affected.
Effects of eutrophication
  • Affects the food chain : The food chains disrupt when toxic chemicals and other pollutants in the water are consumed by aquatic animals (like fish, shellfish etc.), which are then eaten by human beings. Example: The occurrence of the Minamata Bay disease in Japan in 1956.


Prevention of Water Pollution:

  • Contaminated water from the factories should not be released directly into the water bodies; rather they should be treated in the water treatment plants to lower its toxicity.
  • Usage of pesticides, herbicides and other agro-chemicals should be minimized to reduce the possibility of contamination in the waterbodies.
  • Dumping of garbage in ponds, rivers, lakes, seas and oceans should be strictly prohibited.
  • Human activities that cause water pollution must be prohibited to keep the waterbodies clean.
  • Lastly, we must use water judiciously and never waste it.
Preventing water pollution 
 Stop polluting water bodies in the world


New Words :

Sewage: Waste materials like faeces and dirty water eliminated from households and factories, which flows away through sewers.

Run-off: Draining away of water from land.

Ecosystem: The interaction between the living and non-living things in a particular region.

Food chain: It is the chain that shows the transfer of matter and energy from one organism to another in the form of food.

Water Treatment Plant: A facility where wastewater is cleaned before releasing it in a waterbody or re-using it in other activities.

Did You Know?

  • Water pollution can be of three types—marine pollution, surface water pollution and ground water pollution.
  • Plastic garbage is one of the significant sources of water pollution. Almost all the oceans have a massive collection of plastic trash.
Plastic pollution in the ocean facts
  • Some of the most polluted rivers across the world are the Ganges (India), Citarum (Indonesia), Yellow River (China), Sarno (Italy) and Buriganga (Bangladesh).
Water pollution for class 4
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