Satellite data show people are overdrawing water from some of the world's largest groundwater basins.
Researchers from the University of California, Irvine say it's unclear how much water is left in the most overburdened aquifers. The problem is expected to worsen with climate change and population growth.
Using measurements taken by NASA's twin Grace satellites, scientists found the most overstressed groundwater basins were located in the driest regions.
Arabian Aquifer System in the Middle East, which serves more than 60 million people, was considered the most stressed in the world followed by the Indus Basin aquifer of northwestern India and Pakistan.
The farm-rich Central Valley in California was considered highly stressed.
The two studies were published online Tuesday in Water Resources Research, a journal of the American Geophysical Union.