Use of large amount of ground has resulted in lowering the ground water level. The widening imbalance between the groundwater depletion rate and depletion of the fresh water aquifers is resulting in lowering of fresh water table. The basic source of pure water available on earth is rainwater. A large amount of rain water is wasted as run off to the oceans. If we can preserve a small fraction of this wasted run-off, we will be provided with a new origin of precious resource.
Rain water harvesting is process of collecting rainwater from the roofs of building and storing it underground for later use. It raises the declining water table. Town planners and civic authorities in many cities in India have made rainwater harvesting compulsory in all new buildings. Water and sewage connections are not given to buildings if they don’t have water harvesting system.
The various methods used for rainwater harvesting are discussed below.
1. Traditional rainwater harvesting: It can still be seen in rural areas where people use storage bodies like lakes, ponds, irrigation tanks etc. to store the water for future use.
2. Modern rainwater harvesting system: It can be categorized as follows.
(i). Artificial recharging: It is a way of natural infiltration of rainwater into the underground geological formation by artificial methods. Methods are devised to collect and store runoff water from roof tops of the buildings, roads, play grounds etc. Only unpolluted surface water should be charged into recharge structures. Urban sewage should be prevented from entering into recharge structures. The various methods of artificial recharging are
· Absorption well method
· Well cum bore method
· Absorption Pit method
· Recharge trench cum injection well
(ii). Rainwater harvesting: The various methods used for rainwater harvesting are
· Bore well with settlement tank
· Percolation Pit method
· Open well method with filter bed sump
Benefits of Rainwater harvesting:
· Reduced water supply demand from external sources.
· Raised ground water level
· Rain water is naturally soft; contain almost no dissolved minerals or salts.
· Increased independence and water security