New Delhi, June 15, 2012: Thrust upon the government as a court order in 2001, rainwater harvesting has been a failure in Delhi. Recently chief minister Sheila Dikshit also accepted that the policy has not managed to achieve the desired results. Essential for a city like Delhi that is largely dependant on neighbouring states for its water supply, rainwater harvesting can be successful if adopted uniformly and on a large scale.

Delhi, June 14, 2012: How much is 69 billion litres of water? By a rough calculation it is equivalent to nearly 9 million water tankers — the same ones that can be seen trundling about supplying precious water to Delhiites in a swathe of residential colonies.

But, 69 billion litres of water is the amount of water that rains on Delhi's rooftops every year. The calculation is simple — take Delhi's average rainfall at about 490 millimetres, and multiply it with the total rooftop area of about 140 square kilometres as estimated by some experts.