Data gathered from 170,000 groundwater monitoring wells and 1,700 groundwater systems over the past 40 years shows that groundwater reserves are dropping at an alarming rate. This seems to be a problem in all parts of the world, from California to Iran to southern Europe.

But there’s also a silver lining. The study also shows that sustainable practices and careful management of groundwater can help replenish reserves.

Water underground

When we think of fresh water, we usually think of lakes and rivers. But much of the water we use actually comes from underground. Around 30% of all the readily available fresh water in the world is hidden in underground rock pores and fractures. This groundwater accounts for around half of the water we drink and close to 40% of the water used for agriculture and industry.

In principle, this water is a renewable resource. It replenishes from surface precipitation and seeping, but if you use too much of it, you can deplete it.

This is precisely what’s happening in many parts of the world.

According to Hansjörg Seybold, a scientists from ETH Zurich, the entire world is using groundwater “like there’s no tomorrow.” Together with researchers from the University of California, Santa Barbara, he painstakingly combed through four decades of data to see how the world is pumping groundwater.

The measurements show that since 1980, groundwater levels have been steadily decreasing almost everywhere. Since 2000, this decline has started accelerating more and more, particularly in arid regions.

“We weren’t surprised that groundwater levels have fallen sharply worldwide, but we were shocked at how the pace has picked up in the past two decades,” Seybold says.

The main culprit for this, researchers note, is agriculture.

Feeding the thirsty world

Globally, around 70% of freshwater is used for agriculture. Some foods (meat, in particular) require much more water than others, but all agriculture is reliant on water — and overall, our agriculture is using more and more water.

To make matters even worse, the world’s population continues to increase, especially in arid places — and climate change is also fueling water shortage.

But it’s not all bad.

“The study also reveals good news,” says co-author Debra Perrone. “Aquifers in some areas have recovered in places where there have been policy changes or where alternative sources of water are available for direct use or for recharging the aquifer.”

For instance, the aquifer beneath lake Geneva in Switzerland (close to the French border) is showing remarkable signs of recovery. In the 1960s, both countries were pumping out water without much consideration. Then, the two countries started coordinated efforts to manage water more sustainably. First, the groundwater was stabilized — then, it started returning to its natural levels. It’s not quite there yet, but it’s an example that groundwater levels can also go up.

However, there’s also a timing issue. These measures work best when the aquifer levels are still relatively high. If they drop below a threshold, it becomes much harder to recover them.

“Such examples are a ray of hope,” says UCSB researcher and lead author Scott Jasechko. Nevertheless, he and his colleagues are urgently calling for more measures to combat the depletion of groundwater supplies. “Once heavily depleted, aquifers in semi-deserts and deserts may require hundreds of years to recover because there’s simply not enough rainfall to swiftly replenish these aquifers,” Jasechko says.

In addition, coastal aquifers are all the more troubled. If the groundwater falls below a certain level, then seawater can start flowing into the aquifer, rendering it unusable for humans and turning it into poison for plants. This is already what’s happening in large areas on the Western US coast.

“That’s why we can’t put the problem on the back burner,” Seybold says. “The world must take urgent action.”

Journal References:

Jasechko S, Seybold HJ, Perrone, D. et al. Rapid groundwater declines in many aquifers globally but cases of recovery, Nature, 2024. doi: external page10.1038/s41586-023-06879-8call_made

De los Cobos, G. The Genevese transboundary aquifer (Switzerland-France): The secret of 40 years of successful management. Journal of Hydrology: Regional Studies, 2018, doi: external page10.1016/j.ejrh.2018.02.003call_made