Rainwater harvesting is a simple strategy by which rainfall is gathered and stored for future usage. The process involves collection and storage of rainwater with help of artificially designed systems, that runs off natural or man-made catchment areas e.g. rooftop, compounds, rocky surface, hill slopes or artificially repaired impervious/semi-pervious land surface. The collected rainwater from surfaces on which rain falls may be filtered, stored and utilized in different ways or directly used for recharge purposes. Rainwater Harvesting is unrestricted from any kind of impurity, with relatively less storage cost and no maintenance cost involved except for periodical cleaning. With depleting groundwater levels and fluctuating climate conditions, this measure can go a long way to help mitigate the adverse effects rising water scarcity. Reserving rainwater can help recharge local aquifers, reduce urban flooding and most notably, ensure water availability in water-scarce zones.

There are two major techniques of rainwater harvesting.

1. Surface runoff harvesting

In this method, rainwater flows away as surface runoff and can be stored for future use. Surface water can be stored by diverting the flow of small creeks and streams into reservoirs on the surface or underground. It can provide water for farming, for cattle and also for general domestic use. Surface runoff harvesting is most suitable in urban areas. Rooftop rainwater/storm runoff can be harvested in urban areas through:

• Recharge Pit 
• Recharge Trench 
• Tubewell
• Recharge Well

2. Groundwater recharge

Groundwater recharge is a hydrologic process where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. The aquifer also serves as a distribution system. The surplus rainwater can then be used to recharge groundwater aquifer through artificial recharge techniques. Rainwater in rural areas can be harvested through:

• Gully Plug 
• Contour Bund
• Dugwell Recharge 
• Percolation Tank
• Check Dam/Cement Plug/Nala Bund 
• Recharge Shaft

Examples of Traditional water harvesting system in India 

• Trans-Himalayan Region

Zing -Tanks for collecting water from melted ice in Ladakh.

• Western Himalayas

Kul -Water channels in mountain areas of Jammu, Himachal Pradesh. Naula -Small ponds in Uttaranchal. 

• Eastern Himalayas

Northeastern Hill Ranges Apatani system -Terraced plots connected by inlet and outlet channels in Arunachal Pradesh. Zabo -Impounding runoff in Nagaland Bamboo drip irrigation – Water from streams in the hills is brought to the plains via bamboo pipes for drip irrigation in Meghalaya 

• Brahmaputra Valley

Dongs – Ponds in Assam Dungs or Jampois – small irrigation channels linking rice fields to streams in the Jalpaiguri district of West Bengal 

• Indo-Gangetic Plain

Dighis -Small square or circular reservoir fed by canals from rivers in Delhi Baolis – secular structured stepwells from which everyone could draw water and use for washing and bathing. 

• Thar Desert

Baoris / Bers -Community wells in Rajasthan Tankas -Underground tank Bikaner in Rajasthan Kund – a circular underground well; having a saucer-shaped catchment area that gently slopes towards the center where the well is situated.

• Central Highlands

Johads -Earthen check dams in Alwar district, Rajasthan

Advantages of implementing rain-water harvesting: 

• Reduced Water Bills 
• Ecological benefit
• Reduces erosion and flooding around buildings 
• An adequate means for Irrigation purpose 
• Reduces demand on Ground Water