The water that supplies aquifers and wells that billions of people rely on around the world is mostly a non-renewable resource that could run out, a new Canadian-led study suggests.
"Groundwater is a super-important resource," Gleeson said in an interview with CBC News. "It's used by more than a third of the world's population every day for their drinking water and it's used by agriculture and industry.
"The amount that was renewable was no more than 1.3 million cubic kilometres or less than six per cent. But the researchers said that was likely an overestimate due to the types of rock in the areas where most of the measurements were taken. Correcting for that suggested that the actual amount of groundwater renewable within 50 years was likely only 0.35 million cubic kilometres, or enough to cover all the land on Earth to a depth of just three metres.
Gleeson said in places like California and the U.S. Midwest, people are already using "non-renewable" water that is thousands of years old and in places such as Egypt, they're tapping into water that may have last been renewed a million years ago. Such old water isn't just non-renewable — it tends to be saltier and more contaminated than younger groundwater.
In addition, overusing groundwater, either old or young, can lower subsurface water levels and dry up streams, which could have a huge effect on ecosystems on the surface, Gleeson added.