Topic outline

    • Water Cycle


      When we keep anything wet in an open area, the water from the wet things changes in water vapor and mixes with the air around. We cannot see the water vapor evaporating as it is color less. This process of changing liquid water into gas or vapor is called Evaporation. Water vapor is the gaseous form of water.

      When we place handkerchief on cloth line outside in windy place or under the sun, it dries faster. This means that wind and heat from the sun helps in evaporation. This is why we hang our wet clothes out in the sun for drying. With the increase in temperature, the rate of evaporation also increases. Evaporation occurs every day in natural as well as in our manmade environment.



      The process in which a gas changes into its liquid state is called condensation. The water vapor condenses when it is very cold. What do you observe when you keep a glass of cold water on hot summer day? We see droplets of water on the surface of the glass. From where does this droplets came? It actually came from the air.  Water vapor in the warm air, changes back into liquid when it touches the cold surface of glass.

      Example: Due on grass in the morning, water droplets on the outside surface of the cold drink bottle, water droplets on the mirror of bathroom after hot shower.


      Water Cycle

      There is limited water on the earth and exists as solid in the form of snow on the mountains, ice in glaciers and ice caps; it exists in the form of liquid in the rivers, ocean, sea and underground water; it exists as gas in the form of water vapor and steam. The total amount of water on the earth is relatively unchanging, and it has remained about the same since our planet's formation. The water is constantly undergoing process of evaporation and transpiration, condensation, precipitation and accumulation. This journey of water is called water cycle. The water cycle, also known as the hydrologic cycle

      The water cycle is made up of following processes:

      Evaporation and Transpiration

      Heat of the sun causes evaporation of water from rivers, lakes and the ocean. The water vapor formed rises and mix up with air. Evaporation is an important part of the water cycle and occurs continuously throughout the nature.

      Plants require water to make their food, which they obtain from the soil. Plants releases water from leaves which evaporates into the air.


      Water vapor evaporates from water bodies in the air, it condenses and changes into tiny droplets and then clouds are formed.


      When these droplets become so dense and heavy, they come back to the earth in the form of rain, hail, sleet or snow. Precipitation is responsible for bringing back the fresh water on the earth.


      When water falls back on earth, it gets collected in the ocean, lakes or river or under the ground.

      Water is continuously recycled on the earth; from water bodies to the sky and down to land, to be transported back to the water bodies again.


      Importance of water cycle

      We use water for drinking and for other purpose. We have limited water on earth and if the water did not come back to us through the water cycle then we would not have fresh water. So, we should use water judiciously and avoid wasting water.

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