Last week, Delhi recorded rainfall enough to meet 13 per cent of its water demand: CSE

The analysis, by the Centre for Science and Environment, showed that in those seven days, Delhi received nearly 118.4 millimetres of rainfall —143% more than the average. Such a heavy spell can produce around 87,000 million litres of water, the analysis showed.

Just a seven-day spell of rain in the national capital, between August 13 and August 19, produced enough wastewater to meet nearly 13% of the city’s daily water demand, analysis by an environmental think tank has found, highlighting the need potential for groundwater recharge.

A view down Rajpath with clouds over India Gate, in New Delhi. (Photo by Sanjeev Verma/ Hindustan Times)

The analysis, by the Centre for Science and Environment, showed that in those seven days, Delhi received nearly 118.4 millimetres of rainfall —143% more than the average. Such a heavy spell can produce around 87,000 million litres of water, the analysis showed.

Sushmita Sengupta, programme manager (water programme), CSE, said the demand for water in Delhi was estimated to be 2,765 million litres per day, or 644,225 million litres (at a rate of 175 litres per capita per day) annually.

“The volume of rainwater generated in the past week, calculated by multiplying the area by the rainfall received and the co-efficient of the rainwater run-off, was almost 13% of the city’s total daily water demand. This was estimated taking into account 18.8 million population of Delhi (according to the 2011 census) and 1,483 square kilometres area,” Sengupta explained.

Using a tehsil-wise assessment of groundwater resources by the Central Ground Water Board (CGBW), CSE also said the total annual groundwater recharge of Delhi was assessed to be 320 million cubic metres (mcm), with annual extractable groundwater resources at 300mcm.

Sengupta implored that such heavy rainfall be used to recharge the city’s groundwater table. To this effect, she added, stormwater drains that carry rainwater should be clean and managed well.

“The urban water bodies are the main recharge points in a city — they act like sponges. They can absorb flash floods as well as recharge groundwater. While rooftop rainwater harvesting systems are very important, they are only dropping in a bucket. We need to harvest water from all our green spaces,” she said.

In a 2015 order, the National Green Tribunal (NGT) made it mandatory to ensure that no government project, including flyovers and bridges, be approved until they have a provision of rainwater harvesting systems.

At present, there are 544 rainwater harvesting systems installed in Delhi Jal Board buildings, 1305 in government buildings, 3,675 in schools and colleges and 1,869 systems in private buildings.

Sumukhi Venkat, a social activist who has worked extensively with the governments of Rajasthan and Madhya Pradesh to promote rainwater recharge methods, said heavily concretised cities were a primary factor behind rainwater going to waste.

“Delhi’s data shows that comparatively deeper water levels are only found in south and southwest districts, but as we come into central, northern and eastern parts, the groundwater levels get shallower. When rainwater falls on a concrete ground, it essentially goes to waste. With more concrete based development, we are only reducing open spaces where soil can absorb rainwater and help regain water,” Venkat said.