NEW DELHI: Did you know that it is mandatory for every household to have a rooftop rainwater harvesting system wherever the groundwater level is below 8 metres?

The Central Ground Water Authority had issued a notification to this effect way back in 2001, with even a deadline of March 2002.

But its poor implementation is evident because you have to struggle hard to even think of a house or a building that has done rainwater harvesting. That's despite the fact that the groundwater level in most urban areas of the country is well below eight metres.

The sight of rainwater gushing into drains is hardly pleasant, more so when a little effort can help in not only meeting a family's water needs but also help recharge the depleting groundwater level.

Rainwater harvesting -- capturing the downpour, storing it and also using it to recharge the underground level -- has hardly caught people's imagination.

"It calls for a little drive. Everyone thinks, why spend money on this when he is anyway getting his daily supply of water. But people do not realize that nothing is permanent," pointed out Ajay Kharbanda, a Delhi resident who has successfully experimented with rainwater harvesting in his house since 2001.

Awarded by the Delhi CM for his efforts, Kharbanda has been collecting rainwater from his rooftop for household use in a storage tank. He also diverts the overflow into an old dried-up tubewell to recharge the water level. The entire exercise cost him just Rs 20,000.

Delhi's geology makes conditions favourable for artificial recharge. An estimate shows that a roof area of only 50 square metres receives annual rainfall of 30,550 litres, of which 18,330 litres can be harvested. The quantum rises exponentially for larger roof areas, which abound in the cities.

"Very little has been done in water reuse and recycling within the buildings as a strategy to reduce the water demand," concedes Delhi Master Plan 2021. The new bylaws have made water harvesting compulsory in all new buildings built on plots of 100 square meters and above.

Buildings with a daily discharge of 10,000 litres or more also have to incorporate wastewater recycling systems and the recycled water must be used for horticulture.

But the compliance with both directives is poor, despite an estimate that around 40% of the water supplied by the Delhi Jal Board is not used for drinking.

In Chennai, people have even drilled bore wells up to 400 feet, most often with little success. Urbanisation, which uses concrete in a major way, has drastically cut down the earlier easy entry of rainwater underground for a natural recharge.

But Chennai, with an annual average rainfall of 1290 mm, has posted quite a few success stories in rainwater harvesting. IIT-Madras, for instance, now has rainwater-harvesting systems in all its hostels. The water is piped into four large wells, which double up as storage tanks as well as help recharge ground water.

Rashtrapati Bhavan, too, has been harvesting rainwater since 2000 and a spokesman described the system as "very efficient, catering to a lot of needs" of the sprawling establishment.

Jamia Hamdard University, Aurobindo Ashram, Mother's International School, Shri Ram School and Janaki Devi Memorial College are other examples of institutions that have successfully taken up rainwater harvesting in the capital.

The Indore model gives 6% rebate in property tax to all those who adopt rain water harvesting, setting up a good example to be emulated elsewhere.

"I do not say that water harvesting can meet all our needs. But it feels really nice that I have done whatever little I could for the cause of environment," said Ruchi Singhal of Delhi, who has been storing rainwater in her house since 2004. "We use the harvested water for cleaning and gardening. It has to grow as a movement," she said.

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