Parts of India are on track for severe water shortages, according to results from Nasa's gravity satellites.
The Grace mission discovered that in the country's north-west - including the capital Delhi - the water table is falling by about 4cm (1.6 inches) per year.
About a quarter of India is experiencing drought conditions, as the monsoon rains have been weaker and later than usual. But weather and climatic factors are not responsible. They say rainfall has not changed, and water use is too high, mainly for farming.
"We looked at the rainfall record and during this decade, it's relatively steady - there have been some up and down years but generally there's no drought situation, there's no major trend in rainfall," said Matt Rodell, a hydrologist at Nasa's Goddard Space Flight Center near Washington DC.
"So naturally we would expect the groundwater level to stay where it is unless there is an excessive stress due to people pumping too much water, which is what we believe is happening."
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