A couple of years ago, when Shekhar Kapur announced his next movie would be based on a futuristic tale about a water famine in Mumbai, it sounded a little too imaginative. A war over water and conflict between those who controlled water resources and those who needed it didn't sound sufficiently realistic.

Today, the plot is more believable. But thanks to the much-delayed yet healthy monsoons this year, Indian rivers and lakes are full once more and have warded off the spectre of water ration cards and a conflict over water rights.

Plainly speaking, the problem lies in the disparity between the demand for and supply of groundwater. At the current rate of groundwater usage, a number of cities, including Delhi, will run out of groundwater by 2015. That's when water scarcity will become a frightening reality.

Currently, India's water requirement is 750 billion cubic meters, and is likely to rise to 1,050 billion cubic meters by 2025. The scene is quite grim. In 1947, the annual per capita water availability was 5,000 cubic metres. Today it has more than halved and is 2,200 cubic meters, a very significant drop.

A case in point is Punjab. The state has harnessed 98 per cent of its irrigation potential and 90 per cent of the cultivated area is irrigated. Canal water meets just 40 per cent of the irrigation requirements. Sixty per cent of irrigation comes from water drawn from innumerable tube wells. Out of the 138 administrative blocks in Punjab, 86 have been declared 'dark zones' or those where groundwater has been over-exploited, 14 as 'grey' or areas with limited exploitation possibilities. Only the remaining 38 blocks have unlimited exploitation possibilities, referred to as 'white' areas.

Interestingly, while most of the 'dark' blocks fall in the agricultural belts of central Punjab, the 'grey' and 'white' blocks fall either in the Kandi area or south-west Punjab, where groundwater exploitation is either difficult due to the sub-mountainous topography or the high salinity of groundwater renders it unusable. This is a clear indication that groundwater availability is strained even in the areas, which have sufficient groundwater reserves.

According to a Central Ground Water Board (CGWB) study, groundwater levels have gone down by more than four metres in 306 districts of 20 states over the past 20 years.

There are several ways of managing water resources. As the source of all water - rivers, ponds, streams, wells and lakes - is the annual rainfall, the depleting levels of groundwater can be stalled and, in time, replenished through judicious rainwater harvesting. India receives approximately 100 hours and 750 mm of rains every year, and it is during this period that rainwater can be harvested, to ensure adequate supply for the rest of the year.

In fact, rainwater harvesting is not new to India. Around 350 BC, rain gauges and rainwater harvesting were prevalent in several parts of India. Arthshastra, the historic politico-administrative treatise by Kautilya, provides for tax benefits for those constructing water-harvesting structures in their homes. While harvesting rainwater from rooftops and the ground was a part of the ancient Indian ethos, it is soon going to be an unavoidable necessity for 'modern' India.

The process is simple and can be installed using low cost and locally available material like stones, mud and bamboo. Structures like pits back-filled with boulders, gravel and coarse sand; trenches filled with filtration material; dug wells, hand pumps, recharge wells and shafts, lateral shafts with bore wells and spreading techniques can be used to replenish groundwater reserves. Capturing the run-off water from rooftops, local catchments, seasonal flood water from local streams and conserving water through watershed management could further help in raising groundwater levels.

Rapidly increasing demands due to explosive population growth and the consequent increase in agricultural activity and industrial development is causing an immense strain on the already depleted groundwater reserves, which continue to decline even further in the absence of groundwater recharging.

The budget for water conservation, though currently inadequate, is not entirely unsatisfactory. The Government of India spends approximately Rs200 crore per year directly, while 70 per cent of the annual expenditure of Rs1,000 crore on EGS (employee guarantee scheme) goes towards water conservation. In the last two years, there has been an additional contribution of Rs258 crore by way of people's participation through voluntary labour or shramdaan in water conservation projects.

The government is taking water conservation seriously at the policy-making level, though actual implementation in a concerted countrywide basis needs to be streamlined and strengthened. Effective October 2002, the Maharashtra state government has made installing rain water harvesting systems mandatory in all buildings being constructed on plots exceeding 1,000 sq.m.

Individual initiatives in Mumbai have shown extremely favourable results. Tata Institute of Social Sciences (TISS) began rainwater harvesting on its campus in 2002. It collects over 3,700 cubic metres of rainwater from the terraces of its buildings, which is used for cleaning, washing and watering its extensive gardens. As a result of the initiative, not only has the campus taken a major step towards water self sufficiency, but the TISS plantations have a survival rate of 95 per cent even during extreme water scarcity.

Similarly, the Textila housing society at Prabhadevi, has adopted rainwater harvesting on the terraces of its four buildings housing 92 flats. Rainwater is collected from the rooftops and stored in two eight feet deep underground chambers. The Ryan International School in Navi Mumbai is also successfully practising rainwater harvesting.

The current water availability scenario in virtually every Indian city including Mumbai is quite alarming. Mumbai has to supply water to its 12 million 'residents' and another two million-strong 'floating' population everyday. BMC's water supply capacity is only 2,900 million litres a day (MLD) while the actual water requirement is 3,400 MLD. According to estimates the gap of 500 MLD a day will rise to over 2000 MLD in less than 15 years.

Yet, ironically, millions of litres of precious rainwater are drained into the sea every year in the absence of water harvesting.