"We're using our groundwater resources too fast—faster than they're being renewed," Dr. Tom Gleeson says in a University of Victoria press release. Gleeson, along with fellow researchers, published the most accurate map of Earth's groundwater supply to date on Monday in Nature Geoscience. The study found there is about 14.3 million cubic miles of groundwater left on Earth. But that's not as encouraging as it sounds, according to Reuters, because no more than 6% of it is renewable within a human lifetime. "That's never been known before," says Gleeson, who adds that people are going to need to manage that resource better as water demands grow amid ongoing drought. "Groundwater can and should be thought of as a very useful buffer to climate extremes," he says. "It's a valuable and strategic resource for mitigating the extreme impacts of climate."
The amount of groundwater less than 50 years old is enough to cover every continent with approximately 10 feet of water, according to the study. But while that young groundwater is more quickly replenished, it's also more easily polluted by people and impacted by climate change, Reuters reports. The rest of Earth's groundwater—which can be millions of years old—is much deeper underground and can be extremely salty and contain harmful elements, according to the press release. The next step is to figure out how dire the situation is. "Since we now know how much groundwater is being depleted and how much there is, we will be able to estimate how long until we run out," Gleeson says. (But at least we might have more helium left that we thought.)