Rain water harvesting generally means collection of rain water. Its special meaning is a technique of recharging of underground water. In this technique water is made to go underground after collecting rain water locally, without polluting the same.
With this, water during the time of scarcity local domestic demand can be met.
Why do we need water harvesting? Three main reasons are responsible for this:
Total amount of rain water recovered in an area is called rain water reserve. Effective management of rain water reserve is called potential water harvesting. For example, consider the area of the roof of the house is 100 square metres and the average rainfall of this area is 60 cm. Suppose the water on the roof has neither flowed, percolated nor evaporated then there will be 60 cm, high water on the roof.
Volume of water = Area of the roof x Amount of annual rainfall
= 100 x 60 cm = 100 x .6 = 60 cubic metres
In other words, a family can collect 60,000 litre water in a year. All water related needs of this family can be met with this. On an average a person needs 10 litre water for drinking daily. If family consists of 6 members, then you need 6 x 10 x 365 = 21900 litres water. Remaining (60,000 - 21,900) = 38,100 litre water can be used in dry weather when there is a scarcity of water.
The tradition of water harvesting is very old in India. But the utility of water harvesting has never been felt so much as it is today. Even today the people living in the areas of water scarcity try to do their domestic work by adopting old methods. Deepening and dredging of wells, tanks and ponds are included in these methods.
Water harvesting in the small channels (locally known as bawli) is an important traditional method in the areas of water scarcity. Now we can be in a better and secure situation by adopting new technique of water harvesting.
If the people living in 5,87,000 village engage themselves for harvesting rain water of their 2000 lakh hectare area, there will be lot of water available for use. On an average a village comes under the radius of 37,500 lakh cubic metre rain water reserve. By this calculation we come to know that there is great potential of rain water harvesting.