List some of the uses of water in various industries and for other commercial purposes.

(i) Water is a very important fluid which is essential for all living beings. Our body contains $70\%$ of water and blood contains $98\%$ of water.

(ii) We need water for drinking, bathing, cooking, washing, etc. It is required in very large amounts for agriculture and in industries.

2. Sources of water :

(i) Surface water consists of oceans and seas, rivers, lakes, streams and ponds.

(ii) Water present in rivers, lakes and streams are formed by melting of snow on mountains and from rain.

(iii) The water collected under the ground is called groundwater.

(iv) The level of water under the ground is called water table.

3. Water cycle :

(i) The natural circulation of water in nature is called the water cycle.

(ii) There are three main processes through which water is released back into the atmosphere and vice versa. They are: evaporation, condensation and precipitation.

(iii) Evaporation is a phenomenon in which the liquid goes into the vapour state at a temperature below its boiling point.

(iv) Condensation is the process in which the water vapour cools down to form tiny water droplets.

(v) The falling of large sized drops on the earth in the form of rain is also called precipitation.

4. Rain doesn't fall for long period : 

Drought is a condition caused by a decrease in level of water in rivers, ponds and lakes. The groundwater may also become scarce.

5. Conservation of water :

(i) The most important method of water conservation is to avoid wastage of water and the process starts at home.

(ii) Dams are built to store water and to prevent flooding during excessive rainfall.

6. Rainwater harvesting :

(i) The process of collecting rainwater and storing it for later use on rooftops of the buildings is called rainwater harvesting.

(ii) Rooftop rainwater harvesting is a traditional technique in which rainwater is collected from the roof top and allowed to go into a storage tank through pipes.

(iii) In drain water harvesting, the rainwater from the roadsides goes directly into the ground into pits, trenches, and dug wells which can be used later.