Rainwater Harvesting

Syllabus: General Studies Paper 3

The NITI Aayog report (2018) says that India’s water demand will exceed water supply by a factor of two by 2030. These call for urgent attention for ensuring water security in the coming years.

• According to World Water Development Report 2015 (UNESCO), India is a frontrunner in groundwater extraction. 
• The water table is going down in several areas. 
• The reasons for this decline are multi-fold;

• Overexploitation of shared water resources, 
• Mismanagement, and 
• Climate change impact.

• India covers around 2.45% of the world’s surface area and has 4% of the world’s water resources.
• In India, rainfall is the primary source of freshwater.
• For a country of its size, India receives the second most amount of rainfall.
• Several metropolitan cities are already facing difficulties meeting water demand due to high population density and limited water resources. 
• For example, Delhi has a water supply of approximately 930 million gallons a day (mgd) while its demand is 1,380 mgd.

Rain Water Harvesting

• Rain water harvesting is collection and storage of rain water that runs off from roof tops, parks, roads, open grounds, etc.
• This water runoff can be either stored or recharged into the ground water. 

A rainwater harvesting systems consists of the following components:

• Catchment from where water is captured and stored or recharged,
• Conveyance system that carries the water harvested from the catchment to the storage/recharge zone,
• First flush that is used to flush out the first spell of rain,
• Filter used to remove pollutants,
• Storage tanks and/or various recharge structures.

Government Efforts to conserve the rainwater

• For improving access to water, the government has given special focus to implementing “source sustainability measures such as

• Recharge and reuse through grey water management 
• Water conservation
• Rainwater harvesting

• A campaign to “Catch the rain, where it falls, when it falls”, which aims to push stakeholders to create appropriate rainwater harvesting structures, has also been launched.
• Several government schemes, for example, Atal Bhujal Scheme, are currently focusing on aquifer mapping to construct artificial reservoirs and rainwater harvesting structures. 
• These mapping techniques take into account hydrogeology and source water availability. 
• These efforts are expected to reduce groundwater depletion. Rainwater harvesting (RWH) process will help in this regard.

Agenda Ahead

• Efforts that could help attain the target of reducing dependency on groundwater, 
• Enhancing water security, 
• Include rejuvenation and 
• Recharge of natural and constructed water bodies, 
• Increased reuse of treated wastewater through local sewage treatment plants and well-designed rainwater harvesting systems across residential and commercial areas. 
• There is a need for stringent policy initiatives for long-term and sustainable solutions. 
• An integrated water management plan must be brought up by local bodies and implemented at the local level. 

Therefore, the need of the hour is to promote rainwater harvesting using a mix of traditional ecologically safe, viable and cost-effective systems with modern rainwater saving techniques, such as percolation tanks, injection wells and subsurface barriers to rejuvenate India’s depleted water resources. But using only traditional methods is not enough. Productively combining these structures could be the answer to India’s perennial water woes.

Traditional water conservation systems around India

• Phad – It is a community-managed irrigation system in the tapi river basin in Maharashtra. It starts with check dam built across a river and canals to carry water to agricultural blocks with outlets to ensure excess water is removed from the canals.
• Zing – It is found in Ladakh, are small tanks that collect melting glacier water. A network of guiding channels brings water from the glacier to the tank.
• Kuhls – They are surface water channels found in the mountainous regions of Himachal Pradesh. The channels carry glacial waters from rivers and streams into the fields.
• Zabo or Ruza System– It is practised in Nagaland. Rainwater that falls on forested hilltops is collected by channels that deposit the run-off water in pond-like structures created on the terraced hillsides.
• Jackwells – The Shompen tribe of the Great Nicobar Islands uses this system, in which bamboos are placed under trees to collect runoff water from leaves and carries it to jackwells which are pits encircled by bunds made from logs of hard wood.
• Pat system – It is developed in Madhya Pradesh, in which the water is diverted from hill streams into irrigation channels by diversion bunds. They are made across the stream by piling up stones and teak leaves and mud.
• Eri – It is tank system, widely used in Tamil Nadu which acts as flood-control systems, prevent soil erosion and wastage of runoff during periods of heavy rainfall, and also recharge the groundwater.
• Johads – They are small earthern check dams used to conserve and recharge ground water, mainly constructed in an area with naturally high elevation.
• Panam keni – The Kuruma tribe (a native tribe of Wayanad) uses wooden cylinders as a special type of well, which are made by soaking the stems of toddy palms and immersed in groundwater springs.
• Ahar Pynes – They are traditional floodwater harvesting systems indigenous to South Bihar. Ahars are reservoirs with embankments on three sides and Pynes are artificial rivulets led off from rivers to collect water in the ahars for irrigation in the dry months.
• Jhalara – Jhalaras are typically rectangular-shaped stepwells that have tiered steps on three or four sides in the city of Jodhpur.
• Bawari – Bawaris are unique stepwells that were once a part of the ancient networks of water storage in the cities of Rajasthan.
• Taanka – It is a cylindrical paved underground pit into which rainwater from rooftops, courtyards or artificially prepared catchments flows. It is indigenous to the Thar Desert region of Rajasthan.
• Khadin – Also called dhora, is a long earthen embankment that is built across the hill slopes of gravelly uplands. It is indigenous to Jaisalmer region and similar to the irrigation methods of Ur region (Present Iraq).
• Kund – It is a saucer-shaped catchment area that gently slopes towards the central circular underground well. It is found in the sandier tracts of western Rajasthan and Gujarat.