'60% of groundwater of Indo-Gangetic basin unusable'

As much as 60% of the groundwater in the Indo-Gangetic basin contains salt and arsenic in high concentration, scientists have warned.

Widespread contamination, rather than depletion of the groundwater, has emerged as a serious cause of concern for millions in Pakistan, India, Bangladesh and southern Nepal, who rely on this basin for their livelihood.

The Indo-Gangetic basin encompasses more than 250 million hectares across these four countries hosting more than 750 million people and constituting over 100 million hectares of agricultural land that accounts for a quarter of global groundwater withdrawal.

While satellite data in the past illustrated sharp drop in the groundwater level in northwest India and parts of Pakistan, a fresh look at the space data with ground level measurement of water clearly indicates that the condition has worsened with degraded groundwater rather than the quantity of water in the ground aquifers.

An international team of scientists found that for groundwater up to a depth of 200 metres,― which represents a volume 20 times greater than the combined annual flow of the Indus, Brahmaputra and Ganges rivers, ― almost 60% of the water is contaminated by arsenic or salt. Of the 30,000 cubic km of groundwater storage estimated in the basin, as much as 23% is estimated to have a salinity greater than 1 gm/litre. A further 37% of ground water contains arsenic in toxic concentration.
“We show the water table has been stable or rising across 70% of the aquifer between 2000 and 2012. Groundwater levels are falling in the remaining 30% (of the ground water storage).

Within 60% of the aquifer, access to potable groundwater is restricted by excessive salinity or arsenic,” the team of 15 scientists from 12 institutes reported in Nature Geoscience.

Scientists from National Institute of Hydrology, Roorkee, and Indian Institute of Technology, Kharagpur, are part of the team that came up with the alarming findings.

“With the right treatment, polluted groundwater can be used for irrigation and drinking. However, first we need to know if a tube well has high arsenic concentrations or other pollutants ― so there needs to be good water testing and monitoring,” team leader Alan MacDonald from the British Geological Survey told DH.