Rainwater Harvesting is a process involving collection and storage of rain water (with the help of artificially designed system) that runs off natural or man-made catchment areas e.g. roof top, compounds, rock surface or hill slopes or artificially repaired impervious/semi-pervious land surface. Undoubtedly a number of factors contribute to the amount of water harvested e.g. the frequency and the quantity of rainfall, catchments characteristics, water demands and the quantum of runoff, and above all speed and ease with which the rainwater percolates through the subsoil to recharge the ground water.

Due to deforestation and the consequent ecological imbalance, the water level beneath the ground is being depleted day by day. As known to all, the constant rising demand of water supply, especially from the urban areas does not match with the surface water sources, as a result of which the water reserves beneath the ground level are overexploited. This consequently results in the water level depletion. Thanks to the selfless endeavor and untiring efforts made by the scientists in the field of hydrogeology, special techniques for recharging ground water level have been developed recently.

Water harvesting, apart from recharging the ground water level, increases the availability of water at a given place at a given point of time. It also reduces the power consumption as 1 m rise in water level results in saving of 0.4 KWH of electricity (as per recent finding). It further reduces the run off which chokes the storm water drains, reduces flooding of water on the roads, improves the quality of water and reduces the chances of soil erosion.

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A Typical Roof Top RainWater Harvesting System comprises of:

  • a. Roof catchment
  • b. Gutters
  • c. Downpipes
  • d. Rain water/ Storm water drains
  • e. Filter Chamber
  • f. Ground Water recharge structures like pit, trench, tubewell or combination of above structure

Rainwater Harvesting is a way to capture the rain water when it rains, store that water above ground or charge the underground and use it later. This happens naturally in open rural areas. But in congested, over-paved metropolitan cities, we need to create methods to capture the rain water.

Rainwater harvesting is a very ancient technique known to have exsisted for over 4000 years. This technique is being revived today to give back to nature what we take from it.

Rain water harvesting - a simple, economical and eco-friendly method of water conservation is an ideal solution to recharge the ground water.

The rainwater that falls on the surface/ roof top is guided to borewells or pits or new/ old/ abandoned wells through small diameter pipes to recharge the underground water which can be used later whenever required.

Rainwater can be harvested to the extent of 55,000 litres per 100sq. metres area per year from rooftops .

In many areas, rainwater harvesting is a necessity, not a luxury. Most deser areas have little to no fresh water resources. As a result, they must depend on rainwater for most of their water needs. Hawaii, Bermuda and St. Croix are all examples. Rainwater harvesting is also required in many arid Southwestern states on all new construction to aid water conservation.

The principle of collecting and using precipitation from a catchments surface.

An old technology is gaining popularity in a new way. Rain water harvesting is enjoying a renaissance of sorts in the world, but it traces its history to biblical times. Extensive rain water harvesting apparatus existed 4000 years ago in the Palestine and Greece. In ancient Rome, residences were built with individual cisterns and paved courtyards to capture rain water to augment water from city's aqueducts. As early as the third millennium BC, farming communities in Baluchistan and Kutch impounded rain water and used it for irrigation dams.

Artificial Recharge Of Ground Water :

Artificial recharge to ground water is a process by which the ground water reservoir is augmented at a rate exceeding that obtaining under natural conditions or replenishment. Any man-made scheme or facility that adds water to an aquifer may be considered to be an artificial recharge system.

Why RainWater Harvesting:

Rain water harvesting is essential because :-
Surface water is inadequate to meet our demand and we have to depend on ground water.
Due to rapid urbanization, infiltration of rain water into the sub-soil has decreased drastically and recharging of ground water has diminished.
As you read this guide, seriously consider conserving water by harvesting and managing this natural resource by artificially recharging the system. The examples covering several dozen installations successfully operating in India constructed and maintained by CGWB, provide an excellent snapshot of current systems.

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RainWater Harvesting Technique :

There are two main techniques of rain water harvestings.
1. Storage of rainwater on surface for future use.
2. Recharge to ground water.

The storage of rain water on surface is a traditional techniques and structures used were underground tanks, ponds, check dams, weirs etc. Recharge to ground water is a new concept of rain water harvesting and the structures generally used are :-

Pits :- Recharge pits are constructed for recharging the shallow aquifer. These are constructed 1 to 2 m, wide and to 3 m. deep which are back filled with boulders, gravels, coarse sand.

Trenches:- These are constructed when the permeable stram is available at shallow depth. Trench may be 0.5 to 1 m. wide, 1 to 1.5m. deep and 10 to 20 m. long depending up availability of water. These are back filled with filter. materials.

Dug wells:- Existing dug wells may be utilised as recharge structure and water should pass through filter media before putting into dug well.

Hand pumps :- The existing hand pumps may be used for recharging the shallow/deep aquifers, if the availability of water is limited. Water should pass through filter media before diverting it into hand pumps.

Recharge wells :- Recharge wells of 100 to 300 mm. diameter are generally constructed for recharging the deeper aquifers and water is passed through filter media to avoid choking of recharge wells.

Recharge Shafts :- For recharging the shallow aquifer which are located below clayey surface, recharge shafts of 0.5 to 3 m. diameter and 10 to 15 m. deep are constructed and back filled with boulders, gravels & coarse sand.

Lateral shafts with bore wells :- For recharging the upper as well as deeper aquifers lateral shafts of 1.5 to 2 m. wide & 10 to 30 m. long depending upon availability of water with one or two bore wells are constructed. The lateral shafts is back filled with boulders, gravels & coarse sand.

Spreading techniques :- When permeable strata starts from top then this technique is used. Spread the water in streams/Nalas by making check dams, nala bunds, cement plugs, gabion structures or a percolation pond may be constructed.

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Diversion Of Run Off Into Existing Surface Bodies

Construction activity in and around the city is resulting in the drying up of water bodies and reclamation of these tanks for conversion into plots for houses. Free flow of storm run off into these tanks and water bodies must be ensured. The storm run off may be diverted into the nearest tanks or depression, which will create additional recharge.

Urbanisation effects on Groundwater Hydrology :

Increase in water demand
More dependence on ground water use
Over exploitation of ground water
Increase in run-off, decline in well yields and fall in water levels
Reduction in open soil surface area
Reduction in infiltration and deterioration in water quality

Methods of artificial recharge in urban areas :

Water spreading
Recharge through pits, trenches, wells, shafts
Rooftop collection of rainwater
Roadtop collection of rainwater
Induced recharge from surface water bodies.

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Computation Of Artificial Recharge From Roof Top Rainwater Collection :

Factors taken for computation :
Roof top area 100 sq.m. for individual house and 500 sq.m. for multi-storied building.
Average annual monsoon rainfall - 780 mm.
Effective annual rainfall contributing to recharge 70% - 550 mm.

Individual HousesMultistoried building
Roof top area100 sq. m.500 sq. m.
Total quantity available forrecharge per annum55 cu. m275 cu. m.
Water available for 5 member Family100 days500 days

Benefits of Artificial Recharge in Urban Areas :

  • Improvement in infiltration and reduction in run-off.
  • Improvement in groundwater levels and yields.
  • Reduces strain on Special Village Panchayats/ Municipal / Municipal Corporation water supply
  • Estimated quantity of additional recharge from 100 sq. m. roof top area is 55.000 liters.

Harvesting RainWater Harvesting Life :

A Noble Goal - A Common Responsibility
Ground water exploitation is inevitable is Urban areas. But the groundwater potential is getting reduced due to urbanisation resulting in over exploitation. Hence, a strategy to implement the groundwater recharge, in a major way need to be launched with concerted efforts by various Governmental and Non-Governmental Agencies and Public at large to build up the water table and make the groundwater resource, a reliable and sustainable source for supplementing water supply needs of the urban dwellers.

Recharge of groundwater through storm run off and roof top water collection, diversion and collection of run off into dry tanks, play grounds, parks and other vacant places are to be implemented by Special Village Panchayats/ Municipalities /Municipal Corporations and other Government Establishments with special efforts.

The Special Village Panchayats /Municipalities/Municipal Corporations will help the citizens and builders to adopt suitable recharge method in one's own house or building through demonstration and offering subsidies for materials and incentives, if possible.

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Attribute Of Groundwater :

  • There is more ground water than surface water
  • Ground water is less expensive and economic resource.
  • Ground water is sustainable and reliable source of water supply.
  • Ground water is relatively less vulnerable to pollution
  • Ground water is usually of high bacteriological purity.
  • Ground water is free of pathogenic organisms.
  • Ground water needs little treatment before use.
  • Ground water has no turbidity and colour.
  • Ground water has distinct health advantage as art alternative for lower sanitary quality surface water.
  • Ground water is usually universally available.
  • Ground water resource can be instantly developed and used.
  • There is no conveyance losses in ground water based supplies.
  • Ground water has low vulnerability to drought.
  • Ground water is key to life in arid and semi-arid regions.
  • Ground water is source of dry weather flow in rivers and streams.
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RainWater Harvesting