Farmers in Asia and North America are over-using underground water reserves, risking the supply for billions of people.
Researchers from McGill and Utrecht universities say that widespread groundwater depletion has recently been reported in aquifers around the world.
They estimate that as many as 1.7 billion people, mostly in Asia, live in areas where groundwater resources or groundwater-dependent ecosystems are under threat.
The team's combined data on groundwater usage in different nations with global hydrology models to develop what they call the groundwater footprint - a new way of measuring water use relative to supply in aquifers around the world.
It's designed as a location-based measure of the sustainability - or lack of it -of human groundwater use around the planet.
"A single example is telling. It takes about 140 litres of water to grow the coffee beans that go into your morning cup of coffee, whether the beans are grown on an arid plateau in Ethiopia or in a Columbian rain forest," say the researchers.
"But the effect of this water use on the supply of available water will be very different. Until now, there has been no way of quantifying the impact of such agricultural groundwater use in any consistent, global way."