Water is drying up at an alarming rate in the United States, China and other major countries, putting us in major danger, says J.S. Famiglietti, an earth sciences professor at the University of California, Irvine.

The groundwater lying below the earth’s surface in soil and aquifers supplies up to one-third of the water used on this planet. It's particularly vital in the case of serious droughts, such as those occurring in California and Brazil now, the Financial Times reports.

But that water is being used up so quickly in parched areas now that it can't be easily refurbished naturally, according Famiglietti, senior water scientist at the NASA Jet Propulsion Laboratory at the California Institute of Technology.

"Many of the largest aquifers on most continents are being mined," he writes in the journal Nature Climate Change. "Without a sustainable groundwater reserve, global water security is at a far greater risk than is currently recognized."

Endangered areas include the High Plains and Central Valley aquifers in the United States, the North China Plain, Australia’s Canning Basin and the aquifers beneath northwestern India and the Middle East.

"Groundwater depletion the world over poses a far greater threat to global water security than is currently acknowledged," Famiglietti writes.

Meanwhile, Rhett Larson, a law professor at Arizona State University, notes water's strategic geopolitical importance.

"The tide of war and peace often turns on water, as is the case with the conflict in Iraq and Syria against the Islamic State of Iraq and the Levant," he writes in an article for The Huffington Post.

"Water security should have a higher priority in U.S. domestic and foreign policy, as water security is a necessary precondition for peace and stability."

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