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Central Water Commission

(Serving the nation since 1945)

Information For Kids

Frequently Asked Questions

  1. What is water?
  2. How much water is on earth?
  3. Why is ocean salty?
  4. What is Hydrological cycle or water cycle?
  5. What is water pollution?
  6. What are effects of water pollution?
  7. What is water conservation?
  8. How can we conserve water?
  9. What is a dam?
  10. Why do we need dams?
  11. What are type of dams?
  12. What is hydropower?
  13. How is hydroelectric power produced?
  14. What are floods?
  15. What is a drought?

What is Water?

Water is life. You can live without food for more than a month, but cannot only live without water for more than a week. In some organisms, (like jellyfish!) up to 90 % of their body weight comes from water.  In human body, nearly 60 % is water - brain is composed of 85 % water, blood is 79 % water and  the lungs are nearly 80 % water. go to top

How much water is on earth?

  • Water covers nearly 75 % of the earth's surface. But 97 % of it is in the oceans and only 3 % of the earth’s water can be used as drinking water. However, major part of it is either frozen in the polar ice caps or locked up in soil. Thus the water that can be utilized by us is only 0.5% of total water on the earth's surface.
  • The total water supply of planet earth is 1335 million cubic km. It simply means that if we can construct a cubic box of length, breadth and height of 1 km  each, we will require 1335000000 such boxes to store all the water. Amazing ! Is’nt it?
  • About 13000 cubic km of water, mostly in the form of water vapor, is in the atmosphere at any one time. If it all fell at once, the Earth would be covered with only about 25 mm of water.
  • Each day, 1150 cubic km of water evaporate or transpire into the atmosphere.
  • Of the freshwater on earth, much more is stored in the ground than is available in lakes and rivers. More than 8,000,000 cubic km of fresh water is stored in the earth in comparison to about 150,000 cubic km of water stored in lakes, inland seas and rivers. Most of groundwater is within a km of the earth’s surface
  • About  18,000,000 cubic km of water found in glaciers and icecaps, mainly in the polar regions and in Greenland.go to top

Why is the Ocean Salty?

The rain that falls on the land becomes slightly acidic due to some dissolved carbon dioxide from the surrounding air. The acid erodes and breakdowns the rock on earth and carries it along in a dissolved state as ions. The ions are carried through the streams and rivers to the ocean. While many of the dissolved ions are used by organisms others are left for long periods of time where their concentrations increase over time. The seawater contains chloride and sodium which make up over 90 % of all dissolved ions in seawater. The seawater contains nearly 3.5 %  of dissolved salts. This makes the ocen water salty.go to top

What is water cycle ?

One special characteristic of water is its ability to change state very easily. It can be found readily on the planet in all of its three forms, solid, liquid, and gas. The earth also has a limited amount of water. That water keeps going around and around, changing its states, in what we call the "Water Cycle" or the hydrologic cycle. The hydrologic cycle takes place in the hydrosphere, a region containing all the water in the atmosphere and on the surface of the earth. The cycle is the movement of water through this hydrosphere.

Now the entire process is very simple, divided in to six parts as shown in the picture

Condensation occurs when water vapor condenses in the atmosphere to form clouds. When the air cools enough, water vapor condenses on particles in the air to form clouds. As clouds form, winds move them across the globe, spreading out the water vapor. When eventually the clouds can't hold the moisture, they release it in the form of precipitation, which can be snow, rain, hail, etc.

The next three stages: infiltration, runoff, and evaporation occur simultaneously. Infiltration occurs when precipitation seeps into the ground. If precipitation occurs faster than it can infiltrate the ground, it becomes runoff. Runoff remains on the surface and flows into streams, rivers, and eventually large bodies such as lakes or the ocean. Infiltrated groundwater moves similarily as it recharges rivers and heads towards large bodies of water. Evaporation is the change of liquid water to a vapor through heat of the sun. Sunlight heats the liquid water in oceans and lakes and change into a gas. Warm air rises up into the atmosphere and becomes the vapor involved in condensation.

The hydrologic cycle continues to move water and keep sources fresh. Without this process life on Earth would be impossible. go to top

What is water pollution?

When toxic substances enter lakes, streams, rivers, oceans, and other water bodies, they get dissolved or lie suspended in water or get deposited on the bed. This results in the pollution of water whereby the quality of the water deteriorates, affecting aquatic ecosystems. Pollutants can also seep down and affect the groundwater deposits. The main sources of water pollution are:

  • Domestic sewage like wastewater and sanitary sewage that is discarded from households.
  • Agricultural Run off like ground water from agricultural fields where chemical fertilizers have been used indiscriminately.
  • Industrial Effluents like Wastewater from manufacturing or chemical processes in industries go to top

Effects of Water Pollution

Water pollution is not only affect the people but also to animals, fish, and birds. Polluted water is unsuitable for drinking, recreation, agriculture, and industry It diminishes the aesthetic quality of lakes and rivers. Contaminated water destroys aquatic life and reduces its reproductive ability. go to top

Health impacts of water pollution

Water-borne diseases are infectious diseases spread primarily through contaminated water. Hepatitis, cholera, dysentery, and typhoid are the more common water-borne diseases that affect large populations in the tropical regions. Exposure to polluted water can cause diarrhea, skin irritation, respiratory problems, and other diseases, depending on the pollutant that is in the water body. Stagnant water and other untreated water provide a habitat for the mosquito and a host of other parasites and insects that cause a large number of diseases especially in the tropical regions. go to top

Water Conservation

Over the years rising population, growing industrialization and expanding agriculture have pushed up the demand for water. So conservation of water has become the need of the day. Rainwater harvesting essentially means collecting rainwater on the roofs of building and storing it underground for later use. It is essential to improve groundwater decline and groundwater levels, arrest seawater ingress, i.e. prevent the sea from moving further land ward, and conserve surface water run-off during the rainy season and urban wastewater go to top

What can you do to conserve water ?

  • Verify that your home is leak-free.
  • Use only as much water as you require.
  • Close the taps well after use.
  • While brushing your teeth do not leave the tap running, open it only when you require it.
  • Take a short shower instead of a bath.
  • Use a washing machine that does not consume too much water.
  • Do not leave the taps running while washing dishes and clothes.
  • Never put water down the drain when there may be another use for it such as watering a plant or garden, or cleaning.
  • Water in which the vegetables and fruits have been washed can be used to water the flowers and ornamental potted plants.
  • At the end of the day if you have water left in your water bottle do not throw it away, pour it over some plants  
  • Don't leave a water hose running.
  • Don't throw trash in ponds, rivers or the ocean. go to top

Dams and Hydropower

What is a Dam?

A dam is a barrier built across a stream or river to stop or check the flow of water and can serve many purposes. Dams can be small, medium or large. Large dams are more complex to build and take a lot of work, power, time and money. A dam can be made of concrete, rocks, wood, or they might be made of earth. Some examples of a large dam are the Bhakra Dam, Sardar Sarovar, Tehri etc. Visit our page on projects to know more about them.
The most important load that a dam must support is the water behind it. How much the water pushes on the dam is called water pressure. Water pressure increases with the depth of the water. As a result, many dams have wider bottom that withstands the great load of the water deep below the surface. go to top

Why do we need Dams ?

Dams store water for irrigation, drinking water, making electricity, and for recreation. Dams can also help control flooding.

You may be receiving drinking water from a dam's reservoir or eating food grown on a farm that was irrigated by a dam's reservoir water or you might be receiving power generated from a hydroelectric plant. River water rises behind dams, forming artificial lakes called reservoirs. The stored water can be used to generate electricity or to supply water for homes and industries, for irrigation, or for navigation. Reservoirs also are good places to fish and play.go to top

Types of Dams

There are different types of dams based on what materials are used and dam design. Engineers use models and computers to figure out how much water a dam will have to support and how big and strong it must be. Then they can decide what sort of dam to design.The kind of dam depends on its location, materials, temperatures, weather conditions, the kinds of soil and rock and the size of dam to be built.

Gravity dams are the largest and heaviest of concrete built dams. These kinds of dams are built with a large base and rely on their weight to prevent the water from tipping them over. Gravity dams can only be built on a solid rock foundation. Most gravity dams are expensive to build because they require so much concrete. Bhakra dam is concrete gravity dam.

Arch dams are supported by the walls of the canyon in which they are built. The arch dam is built in a curved arch facing the water. Arch dams are good for narrow, rocky locations. Their curved shape holds back the water in the reservoir. Arch dams are thin and require less material than any other type of dam. Arch dams can only be built in narrow canyons where the rock walls are solid and steep. The water pushing on the dam helps secure the dam into place. Idduki dam in India is the only arch dam in the country.

Embankment dams are usually earthen dams or rockfill dams. They are massive structures made of earth and rock that rely on their heavy weight to resist the force of the water. A layer of clay or concrete may be used to stop leaks through gaps in the rocks.Because earth is not as strong as concrete, earthen dams are very thick. Tehri is an example of rockfill dam. go to top

Dams and Hydroelectric Power

Some dams are built specifically to produce hydroelectric power, which is electricity generated from water. This sort of power is very efficient and pollutant-free and costs the least. hydroelectric power plants are able provide electricity at a reasonable cost to families, schools, farms, factories, and businesses.Water is carried by huge pipes to a powerhouse which is usually located by the dam. At the powerhouse, the power of the water pushes turbines around and around and this continued motion creates a force that produces electrical energy.

The electrical energy that is generated at the power plant is a result of converting the potential energy of the water behind the dam into electrical energy. This hydroelectric power is then collected and distributed to homes where it is used to watch TV, play on the computer, cook food, etc. go to top

How is hydroelectric power produced?

Hydropower plant is an arrangement to produce electricity from kinetic energy of falling or fast-flowing water. In the generation of hydroelectric power, water is collected or stored at a higher level and led downward through large pipes (called penstocks) or tunnels to a lower level. The falling water rotates turbines. The turbines in turn drive generators in which an armature coil is rotated in strong magnetic field. This converts the turbine’s mechanical energy into electricity. Transformers change the alternating current produced by the generators into a very high-voltage current that is suitable for long-distance transmission. The structure that houses the turbines and generators, and into which the pipes or penstocks feed, is called the powerhouse. go to top

Hydroelectric power has certain advantages over these other sources: it is continually renewable owing to the recurring nature of the hydrologic cycle; and it produces neither thermal nor particulate pollution. The water after generation of electricity can be used for irrigation and drinking purposes. However the hydropower plants can be constructed only at limited places, require large investment and time. They submerge the large area and cause social and environmental problems. The Government rehabilitates the villagers whose land is submerged.

What are Floods?

Floods are natural disasters which are usually caused by intense rainfall that produce runoff more than a normal holding capacity of river. This cause rivers to overflow their banks and inundate the plains. Floods can last from few hours to few days but cause extensive damage to lives, property and crops.

Floods can be caused by various events such as:

  1. Prolonged rainfall over several days
  2. Heavy rainfall over a short period. Flash floods are caused by this event.
  3. Sometimes a landslide blocks the river or stream and cause it to overflow
  4. Rivers can also flood when dams fail Flood


  1. Flood-control dams have been built on many streams and rivers to store storm runoff and reduce flooding downstream. This is done by temporarily storing the storm runoff and releasing it in moderate quatities when river levels have fallen.
  2. Levees are artificial river banks built to control the spread of flood waters and to limit the amount of land covered by floods. go to top

What is a Drought?

A drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. There is no clear cut demarcation that can define a drought. Droughts can be of three kinds:-

(i) Meteorological drought: This happens when the actual rainfall in an area is significantly less than the climatological mean of that area. The rainfall categories for smaller areas are defined by their deviation from a meteorological area's normal rainfall -

Excess: 20 per cent or more above normal
Normal: 19 per cent above normal - 19 per cent below normal
Deficient: 20 per cent below normal - 59 per cent below normal
Scanty: 60 per cent or more below normal
The country as a whole may have a normal monsoon, but different meteorological districts and sub-divisions can have below normal rainfall.

(ii) Hydrological drought: A marked depletion of surface water causing very low stream flow and drying of lakes, rivers and reservoirs

(iii) Agricultural drought: Inadequate soil moisture resulting in acute crop stress and fall in agricultural productivity

Earlier years of all-India drought 1987, 1979, 1972.

Periods of drought can have significant environmental, economic and social consequences. The most common consequences include:

  • Death of livestock.
  • Reduced crop yields.
  • Shortages of water for domestic and industrial users.
  • Malnutrition, dehydration and related diseases.
  • Famine due to lack of water for irrigation. go to top