A human being without water is a dead human being, which makes NASA's latest data on the world's water supply pretty chilling. About 35% of the fresh water people use comes from large underground aquifers, but supplies are dwindling, with more water removed from 21 of the world's largest 37 aquifers over a decade than replenished. Thirteen aquifers are in serious distress. "The situation is quite critical," head researcher Jay Famiglietti says. Beginning in 2003, NASA's GRACE satellites identified underground aquifers by measuring Earth’s gravitational pull, taking note of where the heavier weight of water wielded a greater pull, then charted changes until 2013, the Washington Post reports. Though the total capacity of the aquifers isn't clear, the data shows some aquifers may be smaller than previously believed. The aquifer under the most stress in the US is California's Central Valley Aquifer, tapped to irrigate farm fields.
"We know we're taking more than we're putting back in—how long do we have before we can't do that anymore?" a researcher tells the Los Angeles Times. "We don't know, but we keep pumping. Which to me is terrifying." The Atlantic and Gulf Coastal Plains Aquifer, across the southeast and Florida, is also depleting, the study finds. Still, aquifers in poor, densely populated areas like northwest India, Pakistan, and North Africa, are in the worst shape. Researchers say the Arabian Aquifer, used by more than 60 million people, shows little to no sign of replenishment. Aquifers take thousands of years to refill as it is. Famiglietti notes there’s an added problem in that people nearest the equator pump more water from aquifers to cope with dry conditions, but that water then evaporates and circulates far away to the north and south. "There's not an infinite supply of water," he concludes. "We need to get our heads together on how we manage groundwater, because we’re running out of it." (Read more water stories.)