A new study finds that nearly one-quarter of the world’s population lives in regions where water is being used faster than it can be replenished. Using computer models of global groundwater resources and water use data, scientists from Canada and the Netherlands calculated that the planet’s “groundwater footprint” — the area above ground that relies on water from underground sources — is about 3.5 times larger than the aquifers themselves. The study found that in most of the world’s major agricultural regions — including the Central Valley in California, the Nile delta region of Egypt, and the Upper Ganges in India and Pakistan— demand exceeds these reservoirs’ capacity for renewal. For example, the groundwater footprint for the Upper Ganges aquifer is more than 50 times the size of aquifer. “This overuse can lead to decreased groundwater availability for both drinking water and growing food,” said Tom Gleeson, a hydrologist at McGill University in Montreal and lead author of the study, published in the journal Nature. According to the scientists, about 1.7 billion people, mostly in Asia, live in areas where water needs for humans and ecosystem services outstrip the ability of aquifers to replenish themselves.