Rain Water Harvesting

About Rain Water Harvesting

Simply put, Rain water Harvesting merely means – ‘Catching and Storing Rain where it falls’. It is a simple technique of collecting rainwater that runs from catchment areas like roofs, pavements, roads, parks, open land etc. and storing it in storage tanks (for immediate use) or in the underground aquifers – natural or man-made for ground water recharge. Thus, rainwater can be stored in tanks and then used for drinking and cooking – as it is done in the desert areas of Rajasthan. Alternatively, it can be done to replenish the groundwater so that the dug wells/tube wells in the area keep on yielding water.

Schematic for Rainwater Harvesting for both storage and groundwater recharge

Schematic for Rainwater Harvesting for groundwater recharge only

A typical RWH system works as shown below:

Rainwater Harvesting helps in the following ways:

• It increases the ground water table. Hence, it helps make defunct tube wells come alive.
• Rainwater harvesting Improves the quality of groundwater,
• RWH reduces tube well pumping cost. Typically every one-meter rise in water level saves about 0.40-kilo watt/hour of electricity while pumping groundwater to the surface
• It helps overcome the inadequacy of surface water to meet our demands and to enhance availability of groundwater.
• Rain Water harvesting, increases infiltration of rain water in the subsoil which has decreased drastically in urban areas due to concretization. Therefore, It reduces water logging and flooding by ensuring that rain water goes in to the ground quickly.
• It mitigates effects of drought
• The cost of recharge to sub-surface reservoir is lower than surface reservoirs. Moreover, subsurface storage space is available free of cost and inundation is avoided
• The ground water aquifer serves as a distribution system also
• No land is wasted for storage purpose and no population displacement is involved
• Ground water is not directly exposed to evaporation and pollution
• Storing water under ground is environmentally friendly
• Reduces soil erosion
• It is easier and cheaper to supply water locally from a recharged groundwater aquifer than to transport it on surface from far off places by way of canals.
• Biological purity of water in the ground water aquifer is very high. Also, temperature variations are minimum.
• It is environment friendly, controls soil erosion and flood and provides sufficient soil moisture even during summer months
• Water stored underground is relatively immune to natural and man-made catastrophes
• It provides a natural distribution system between recharge and discharge points
• It is an ideal system to conserve water and ensure sustainability of water supply, especially where no readily available source of surface water supply exists.

How much can Rain Water Harvesting really help?

To answer this question, let us examine how much water can be harvested…

• A concrete, tiled and paved area of 100 m. sq. size yields about 55 thousand liters of rain water annually (for NCT Delhi) for recharge to ground aquifers.

• Even 75% effective harvesting of above will give about 40 thousand liters of water per year

This is about four times the annual drinking water requirement of a five member family.

The design of a typical Rainwater Harvesting structure with bore well is as given below:

This brings us to the next logical question Why Rain Water Harvesting?