Rain water flows down the hills in the form of small streams which join together to form rivers and lakes. And this is the important and the natural source of water for the living beings. Some of the rain water percolates down the earth until it reaches the hard surface.
There it collects to form a large underground water reservoir. Such water is obtained on digging wells and it is called sub-soil water or ground water. Thus, there are three important natural sources of water besides abundantly available sea water. The sea water being saline can not be sued as such either for industries or for domestic consumption.
(a) Rain water or snow water.
(b) Surface water (river, lakes, streams, canals, ponds, etc.)
(c) Ground water or sub-soil water wells and springs.
In urban areas, the construction of houses, footpaths and roads has left little exposed kuchha earth for water to soak in. In parts of the rural areas of India, flood water quickly flows to the rivers, which then dry up soon after the rains stop. If this water can be held back by storage or by reducing speed of flow, it can seep into the ground and recharge the ground water supply.
This has become a very popular method of conserving water especially in the urban areas. Rainwater harvesting essentially means collecting rainwater on the roofs of building and storing it underground for later use.
Not only does this recharging arrest ground water depletion, it also raises the declining water table and can help augment water supply. Rainwater harvesting and artificial recharging are becoming very important methods. It is essential to stop the decline in ground water levels, arrest sea-water ingress, i.e., prevent sea-water from moving landward and conserve surface water run-off during the rainy season.
Town planners and civic authority in many cities in India are introducing by-laws making rainwater harvesting compulsory in all new structures. No water or sewage connection would be given, if a new building did not have provisions for rainwater harvesting. Such rules should also be implemented in all the other cities to ensure a rise in the groundwater level.
Realizing the importance of recharging ground water, the CGWB (Central Ground Water Board) is taking steps to encourage it through rainwater harvesting in the capital and elsewhere. A number of Government buildings have been asked to adopt water harvesting in Delhi and other cities of India.
All you need for a water harvesting system is rain, and a place to collect it. Typically, rain is collected on rooftops and other surfaces, and the water is carried down to where it can be used immediately or stored. You can direct water run-off from this surface to plants, trees or lawns or even to the aquifer.
Some of the benefits of rainwater harvesting are as follows:
I. Increases water availability
II. Checks the declining water table
III. Is environmentally friendly
IV. Imporves the quality of ground water through the dilution of fluoride, nitrate, and salinity
V. Prevents soil erosion and flooding, especially in urban areas