Contamination Threatens One of the World’s Biggest Freshwater Supplies

Aug 29, 2016

Emily J. Gertz is an associate editor for environment and wildlife at TakePart.

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Three-quarters of a billion people across four South Asian nations rely on one vast water basin for much of their irrigation and drinking water. Called the Indo-Gangetic Basin, it stretches east to west over 618 million acres, sitting like a cap over the Indian subcontinent, and contains about 7,200 cubic miles of groundwater, roughly 20 times the annual flow of the region’s Brahmaputra, Ganges, and Indus rivers combined.

Satellite measurements collected since 2002 have led to worries that the region’s aquifers were being severely depleted by overuse, increasing vulnerability to failed harvests, skyrocketing food prices, and civil unrest.

But in a new study that includes on-the-ground measurements from 3,429 water wells across the basin over multiple years, an international team of scientists has found that water quality, not quantity, is a much bigger problem.

More than 60 percent of the Indo-Gangetic Basin is too contaminated with salt or arsenic to be safe for drinking or agriculture, according to research published Monday in the journal Nature Geoscience.

The basin provides communities and cities in Bangladesh, India, Nepal, and Pakistan with a quarter of all global groundwater that humans extract from underground. The region contains the world’s fastest-growing megacities, including Dhaka and Delhi, as well as the world’s largest aboveground irrigation system: more than 62,000 miles of canals that divert water from the Ganges and Indus rivers for agriculture.

“We worked with teams of scientists in Pakistan, Bangladesh, India, and Nepal—scientists working in the country who brought together data already being measured in these countries,” said hydrogeologist Alan MacDonald of the British Geological Survey, who led the study. “This was the first time at this scale that these scientists had pooled data across the whole of the aquifer.”

Salt concentrations have risen in Pakistan and more arid areas of northwest India, MacDonald said, in part because of the heavy use of the Ganges and Indus rivers for irrigation. “If you tap these rivers, which would naturally flow out to the sea with their natural salt content, [that] accumulates their salt content, which just gets flushed back into the groundwater,” he said.

“Where we looked we found problems with nitrates and pesticides,” MacDonald added, but “there wasn’t enough data for us to map them out across the whole region.”

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Another problem is increased “pumping groundwater at depth, which can be drawing in saline water into higher depths of the aquifer,” he said.