Groundwater is helping to feed the world, but it is dangerously depleted


Much underground water is poisoned, too

Feb 28th 2019Print edition | Special report

IN 2004, WHEN Danmanti Devi was four years old, her mother took her to see a doctor because of pains in her legs. The doctor wrongly diagnosed polio. He could do no more than prescribe painkillers. Danmanti’s legs are now deformed. Many others in Churaman Nagar, her 140-household hamlet of mud huts and a few “pukka” brick houses in rural Bihar, one of India’s poorest states, also hobble on the knock knees or bow legs characteristic of a condition known as skeletal fluorosis. She is one of millions of Indians to suffer this, and to have contracted it merely from drinking water containing dangerous levels of fluoride. She is a victim of the over-exploitation of India’s groundwater.

Fluoride, like arsenic, is present naturally in groundwater. It is harmless (or even beneficial) in small concentrations. The World Health Organisation (WHO) suggests a limit of 1.5 milligrams per litre. In Churaman Nagar, the water that comes from standpipes overseen by the local panchayat (village council) has 16mg.

The hamlet’s inhabitants are among India’s most downtrodden. They are dalits, once called “untouchables”, at the bottom of the Hindu caste system. They eke a living as wage labourers in nearby brick kilns or by distilling moonshine.

In being poisoned by their drinking water, however, they are sadly typical. The most obvious danger—bacterial pollution—is a “second-order problem”, says V.K. Madhavan, chief executive in India for WaterAid, a British charity. More fundamental is contamination by arsenic, nitrates, salinity and fluoride. Some of this is natural, some a consequence of industrial effluent, and of seepage from landfills, septic tanks, leaky underground gas tanks and the overuse of fertilisers and pesticides. But the most intractable difficulty is the pumping of groundwater from ever deeper below the surface. The deeper the water, the more likely it is to be contaminated by chemicals such as arsenic seeping downwards.

As long ago as 2002, the WHO called the effects of arsenic contamination of groundwater in Bangladesh “the largest mass poisoning of a population in history”. Tens of millions are at risk in neighbouring India, too. Efforts to save people from the bacterial diseases carried by surface water leave them condemned to longer-term dangers hidden in the groundwater. Arsenic has been linked to cancers of the skin, gallbladder and lungs.

In the scheme of things, the extraction of groundwater for drinking and bathing by India’s poor, like those in Churaman Nagar, is a minor cause of its over-exploitation. Far more important is irrigation. Almost 60% of India’s irrigation needs are now met from groundwater. The Green Revolution which, in the 1970s, transformed India’s ability to feed itself and turned it into a big food exporter, relied on tube wells, powered by electric pumps.

It also turned India into the world’s biggest extractor of groundwater. The five largest such users, which include America, China, Iran and Pakistan, account for 67% of total extractions worldwide. In India, the water is free. A law from 1882 gives every landowner the right to collect and dispose of all water on and under his land. The cost of the electricity needed to pump it ever farther to the surface is one constraint. But Indian politicians love to lavish cheap or free electricity on rural voters when elections loom (as, in India, they often do). The Green Revolution saw agriculture’s share of total energy use climb from 10% in 1970 to 30% by 1995.

This freed many farmers from the fickle monsoon—India usually receives more than 70% of its annual rainfall in the annual downpours from June to September. In Churaman Nagar, and elsewhere in Bihar, residents believe the rains are weaker than they were, though scientists have so far measured only a tiny decline in the rains in recent years.

In India and elsewhere the easy availability of groundwater has encouraged the cultivation of thirsty crops in water-stressed areas. Starting under British rule, irrigation canals and groundwater-extraction turned the arid lands of Punjab into India’s agricultural powerhouse. Similarly, in China, the dry plains of the north-east now produce 60% of the country’s wheat and 40% of its maize on an area with 4% of its water resources.

As Sunil Amrith, a historian at Harvard University, notes in his new book, “Unruly Waters”, the half-century since the 1960s has reversed a centuries-old pattern in which agrarian wealth lay where rains were most abundant. Instead, Israel, Punjab and Manchuria have actually become net exporters of water, if you include what hydrologists call “virtual” water used in the production of a crop or good. In other words, they sell more water in the form of crops and products than they import in that form or extract from their own sources of water. Mr Amrith notes the “most bitter of ironies” in this agricultural miracle: intensified production means that more land is planted with crops, which reflect more solar radiation than forests. The land becomes cooler, weakening the temperature differences with the sea that drive the circulation of the monsoon. So measures taken to protect farmers from the vagaries of the monsoon have in fact themselves helped make the rains more fickle.

This phenomenon is not confined to India. Across the world, the need for more food production encourages deforestation and the use of more land for agriculture. That in turn will increase demand for irrigation which, as precipitation becomes more erratic and surface water is over-used, will probably rely ever more on groundwater. The long-term impact of this is uncertain. Research led by Mark Cuthbert, of the School of Earth and Ocean Sciences at Cardiff University, found that groundwater systems are likely to take far longer fully to respond to differences induced by climate change than does surface water. Only half the world’s groundwater flows are likely to find a new equilibrium within 100 years. The arid regions where water is scarce are often where response times are longest. So the full impact of withdrawals now may not be felt for decades, or much longer in some cases.

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