Simple Methods of Rain Water Harvesting

The shortage of water even for drinking purpose is a common phenomenon throughout the world, especially in developing and underdeveloped countries.

When the rain water falls on the ground, some of it seeps into the soil but the surplus adversely flows out as a stream or as run-off. The topsoil however, can hold only a fraction of water that falls on it and the rest gradually percolates down, depending on the type of the soil and joins the aquifers, that is groundwater-bearing formation.

When the average rainfall is 1000 mm, approximately 10, 000 litres of rainwater gets collected in one acre of land after evaporation.

The quantity of seepage, in one way or the other, depends upon the soil conditions, The percolated water joins aquifers and this percolation contributes enormously to the building of the ground water table. Arlificial recharge is a process of augmenting the underground water table by artificial infiltration of rain water and surface run-off.

Some of the significant techniques of Rain water Harvesting have been described in brief hereunder.

· In open grounds, the topsoil I s removed and filled with river sand. As the river sand is loosely packed, it allows water to percolate down quickly.

· To make more water to percolate down the soil, percolation pits are made, when there is a paved pathway and are covered with perforated concrete slabs wherever necessary. Whenever the depth of clay soil is more, recharge through percolation pits with bore is preferable.

· Roof tops of houses serve as excellent and economical form of collection centres for rain water. If properly diverted and used for artificial recharge it will augment the ground water table to a sufficient extent. The roof is connected to the well through a filtering arrangement by PVC pipe. A valve system can be incorporated to flush the initial part of the rain water to get rid of impurities collected on the roof. Rain water also can be collected and stored in large s umps to consume directly after necessary chlorination.

· Bathing and washing water can be routed to the open ground nearby to percolate down to retain the soil moisture. The grey water can also be treated by some water treatment methods like Soil Aquifer Treatment System (SAT) and further the pretreated water.

· The ground level near the gate should be raised to retain as much water as possible inside the compound. Alternatively, it is recommended to construct a sloping gutter across the gates and direct the rushing water towards percolation pit. For multistoreyed building, it is better to direct this water to a recharge well.

· The storm drains inside the premises should have boundary wall to ensure that the rain water instead of rushing inot the drains and going as waste, stagnates over the ground for sometme and seeps into the soil.

· Wherever there is a slope, it is recommended to construct a dwarf wall to a height if 1 ft, ti aviud run-off as well as to retain the rain water and allow for slow percolation.

· The run-off water generated in monsoons within an area can be well utilized for ground water recharging by diverting it into suitably designed recharge structures in public parks, splay grounds, stadiums, airports, stations, temple tanks, etc.

· Storm water drains should be designed in such a way that two separate segments are made so as to accommodate water c oming from huses and from roads. The segments on the sides of the roads should be covered with perforated slabs and should have percolation pits of depth 20 to 50 ft., depending on the soil condition, at regular intervals.

· Huge quantity of sewage water which gets generated from the domestic segment can be separated and treated through Aquatic Treatment System (ATS) by cultivating water hyacinth on the sewerage water or applying Biological Treatment using 'Actizyme' pellets. This treated water can be used for recharging water sources like dry rivers for irrigation purpose.

· Due to severe depletion of ground water table, many open wells, bore wells and hand pumps are getting dried. Instead of discarding these wells, they can be converted into useful recharge wells. Roof water and run-off water can be diverted into these wells after filling the wells with pebbles and river sand. There should be an effective arrangement for desalting before diverthing the water into these wells.

· It is explicit that rain water collected from terrace of row of buildings may be led into the nearby ponds through pipelines for recharging the ground water aquifers. Run-off water can also be diverted into this pond after proper desilting arrangement.

· In Industrial set ups, rain water collection from the roof area can be favourably used for coolants and cutting oil. Needless to mention, the treated water from the effluent treatment plant can be utilized for maintaining the greenblet. In a sticker sense, rain water from the monsoons should be made to percolate through the soil to dilute the underground water to minimize the adverse effects of the water from the effluent treatment plant.

· It is advisable to have numerous percolation pits in agriculfure lands for gradual percolation and recharging of aquifer. Construction of small bunds on slope areas slows down the run-off water and helps easy percolation. Run-off water can be diverted into a large well through a Baby well and filtering tank to avoid silt depositing in the well.

Rain water harvesting is not a new concept as for as India is concerned. Our ancestors had been doing it according to the means available then. Nevertheless, slowly with the advent of top water, rain water harvesting has lost its importance. As our State is in a situation where efficient management of water resources has become a necessity, rain water harvesting has come to limelight again. We have to resort to long-term measures in harvesting the rain water due to the growing demand. It is hence emphasized that rain water harvesting should become an integral part of every home, society, village, city and country.