Rainwater harvesting: Here' how Delhi can cure its woes

With rapid urbanisation, the demand of potable water in Delhi is increasing at an alarming rate. Available potable water is not sufficient to meet the growing demands of Delhi. According to the Delhi Jal Board (DJB), the city's water requirement in 2015 was 3,800 MLD (million litres per day), whereas, the total water supply from all sources was 3,400 MLD, indicating a potable water crisis.

To meet the current demand of water (approximately 240 litres per capita per day), Delhi extracts more groundwater than what is recharged and, as a result, groundwater has depleted 10-20 metres in the last decade (Central Groundwater Board). As per the latest estimate, the annual groundwater withdrawal rate is around 479 MCM (million cubic metre) against 281 MCM of natural recharge by rains, which results in rapid depletion of groundwater level. Moreover, with the increasing urbanisation, soil-rain interaction has been severely affected, thus impacting recharge of groundwater and adding to the woes of depleting ground water.

Every year, particularly during summers, Delhi faces a severe water crisis as the demand of potable water increases and the water supply from neighbouring states (one of the important source of water) is reduced. To meet the drinking water demand, DJB supplies water through tankers to the localities that are not yet covered under piped water supply. The parched city witnesses many conflicts because of limited or no supply of water during summer. People living in undeveloped areas or slums have inadequate water as they are mostly dependent on depleting groundwater resources or irregular tanker-supplied water.

To tackle these problems of demand-supply gap, erratic and inadequate supply, the Delhi government has taken several initiatives to improve water supply and has also encouraged people to undertake rainwater harvesting and storage in residential apartments, individual houses, corporate buildings and industrial plants. DJB is involved in generating awareness amongst people for installing rainwater harvesting structures in their localities, particularly in dark zones (the south and southwest districts).

Based on the rainfall intensity in Delhi, the potential estimated for rainwater harvesting is around 183,300 litres from an area of 500 meter square; the potential that the national capital can realise is much more than this estimated figure.

Recently, installing rainwater harvesting systems has been made mandatory by Delhi High Court for plots sized 500 sq m or more, and not following the order will attract higher water bills (1.5 times). The National Green Tribunal has also passed an order to Central Ground Water Authority, DJB and Delhi Pollution Control Committee for installation of rainwater harvesting system for hotels, hospitals and malls, vide order dated March 23, 2016.

The rainwater harvested and stored in underground tanks can be used for recharging aquifers, which can help improve the groundwater level or can be used for domestic purpose and for other uses like irrigation. Moreover, rainwater harvesting is one of the best storm water management practices as it helps improve drainage system during intensive rainfall periods such as monsoon. With frequent spells of intense rainfall, Delhi faces the issue of water-logging, which leads to traffic chaos and other inconvenience. Managing the source of the problem-excessive rainwater-could be an answer to this growing challenge.

For locations with inadequate or depleting groundwater or surface water resources, rainwater harvesting offers an ideal solution. Also, the Yamuna flood-plain, comprising 97 sq km of land, offers good scope for recharging groundwater resources. Out of 580 MCM of rainfall, 280 MCM of monsoon season flow estimated for Delhi goes unutilised due to lack of storage capacity.

Rainwater harvesting has proved to be a game-changer for Chennai which, in 2001, made it compulsory for all residential complexes; as a result, it has over 5 lakh rainwater harvesting systems-the highest for any city worldwide. The groundwater level of the city has also improved (an 1.30 m increase). Bangalore has also made rainwater harvesting compulsory in all buildings. In Delhi, for increasing rainwater harvesting adoption, there is a need for increasing awareness among the public, providing financial incentives and training for installing and using this technology.

After considering the success stories from the southern cities, it will not be incorrect to say that if Delhi has to cope with its water crisis, rainwater harvesting is one of the most cost-effective and sustainable solutions. This can help solve a multitude of the challenges faced by the city currently, including storm water management, depleting groundwater resources and widening demand-supply gap.