Of all the activities that need water, far and away the thirstiest is farming. Cut the use of irrigation water by 10%, it is said, and you would save more than is lost in evaporation by all other consumers. Yet farming is crucial. Not only does it provide the food that all mankind requires, but it is also a great engine of economic growth for the three-quarters of the world’s poor who live in the countryside. Without water they may return to pastoralism-as some people already have in parts of the Sahel in Africa-or migrate, or starve. With water, they may fight their way out of poverty.

Surface water, though, is not enough to meet farmers’ needs. In the United States total withdrawals of water remained steady between 1985 and 2000 but groundwater withdrawals rose by 14%, mainly for agriculture, and in the period 1950-2000 they more than doubled. This was not all for the arid West. Midwestern Nebraska now ranks above California and Texas as America’s most irrigated state. Europe, too, increasingly relies on groundwater, as does the Middle East. In a network of pipes that Colonel Muammar Qaddafi has called the eighth wonder of the world, Libya is drawing fossil water that has lain undisturbed for centuries. Many hydrologists think it will be all but exhausted in 40 years.

It is India, though, that draws more groundwater than any other country. The 230 cubic kilometres that it pumps each year account for over a quarter of the world total. The tripling of Indian groundwater use since 1965 has been stimulated not just by growing demand for food but also by the lamentable public service provided by state governments and the relative cheapness and convenience of a private tubewell. By 2001 India had about 17m of these (and Pakistan 930,000 and Bangladesh 1.2m). The pumps for the wells are usually cheap to run because electricity is subsidised in most places, and in some it is free, though at times it is not provided at all; that is how water is rationed.

The proliferation has brought prosperity and an almost lush landscape to places like Punjab, which grows over half of India’s rice and wheat. But out of sight, underground, there is trouble. Water is being extracted faster than it is replaced and levels are falling, often by two or three times the officially reported rate, according to Upmanu Lall, of Columbia University. The World Bank says the groundwater in 75% of the blocks into which Punjab is divided is overdrawn. Over half the blocks of five other states-Gujarat, Haryana, Maharashtra, Rajasthan and Tamil Nadu-are judged to be in a critical or semi-critical condition, or are similarly over-exploited. Up comes the poison

One consequence is that the water now being pumped is often salty and sometimes high in concentrations of naturally occurring poisons like arsenic, fluorides and uranium. In the village of Bhutal Kalan in Sangrur district, for instance, the farmers complain not just of water levels dropping by two metres after each of the two harvests a year but also of fluorosis, which may cause mottling of the teeth and skin, or, in its skeletal form, arthritic pain and bone deformities. Cancer is also rising, which the farmers blame on the natural poisons and on pesticides, which they apply specially heavily if they grow cotton.

The farmers’ woes do not end there. Though part of the Sangrur district suffers from a falling water table, the other part suffers from waterlogging. This is a common problem when poorly drained soil is over-irrigated, which results in plants’ roots being starved of oxygen, knocking perhaps 20% off a field’s productivity. Sometimes standing water will evaporate, leaving the soil salty as well as saturated.

Tushaar Shah, in “Taming the Anarchy”, his book on water in South Asia, says the groundwater irrigation boom in India is “silently reconfiguring” entire river basins. But of more immediate concern to the farmers are the economic and social consequences of overdrawing groundwater: falling yields, higher electricity costs, ever greater debts, even rising crime among the unemployed. Increasingly, say the farmers, they must look to other, part-time jobs, like driving a taxi. Or they must sell their land. Usually it will go to a village bigwig, perhaps with a little help from local officials.

The main winners, though, are the arhtiyas, the commission agents who act as middlemen between farmers and wholesale buyers and at the same time moonlight, sometimes extortionately, as moneylenders. Few farmers, big or small, are free of debt, and worries about interest payments have driven thousands of Indian farmers to suicide in recent years, many more than the official figures suggest, says Chander Parkash, an academic who helps to run a local NGO for farmers.