new groundwater map

The first map showing the world’s hidden groundwater was published on Monday, bringing us closer to estimating how much there is, and when it will run out if we over-use the resource.

Using data and computer models, an international team of researchers estimated that less than six percent and perhaps as little as one percent of water found close to the Earth’s surface is renewable in a human lifetime.

“This has never been known before,” Tom Gleeson of Canada’s University of Victoria and the lead author of the study, said in a statement.

“We already know that water levels in lots of aquifers are dropping. We’re using our groundwater resources too fast – faster than they’re being renewed.”

The study, published in the journal Nature Geoscience, estimated a total volume of underground water to be almost 23 million cubic kilometres, of which 0.35 million cubic kilometres is younger than 50 years old.

Underground water is found beneath the Earth’s surface and is recharged by rain, snow or water that leaks from the bottom of lakes and rivers.

Its age can be a few months to millions of years. It can be found as deep as 30,000 feet (around 9 km), according to the United States Geological Survey (USGS).

“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 said.

This map is part of the Soil Agricultural Groundwater Banking Index, which identifies farmlands with the most potential to capture groundwater and help recharge the aquifer. (UC Davis graphic)

This map is part of the Soil Agricultural Groundwater Banking Index, which identifies farmlands with the most potential to capture groundwater and help recharge the aquifer. (UC Davis graphic)

Although water found closer to the surface is being renewed quicker than the water found deeper in the Earth, it is more sensitive to contamination and climate change, but it can also serve to temper climate extremes, Gleeson said.

Water found deeper in the Earth is often used for agriculture and industry. It can contain arsenic or uranium and is often more salty than seawater, he added.

“Groundwater can and should be thought of as a very useful buffer to climate extremes,” Gleeson told the Thomson Reuters Foundation in a phone interview from Canada.

“If properly managed it flows to rivers during times of drought so it’s a valuable and strategic resource for mitigating the extreme impacts of climate on water availability.”

According to the study, most groundwater is found in tropical and mountainous regions, with some of the largest deposits in the Amazon Basin, the Congo, Indonesia and along the western borders of North and South America.

Not surprisingly, the least amount is in arid regions such as the Sahara. (Reporting by Magdalena Mis; Editing by Ros Russell; Please credit Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women’s rights, corruption and climate change. Visit

The Canadian Press recently spoke with Gleeson about his team’s findings.

Why should we care about groundwater?

The simplest answer is because over a third of humans drink groundwater every day and we use it for irrigated agriculture around the world. It’s a hugely important, critical resource for both drinking water and for growing food.

What’s the difference between young and old groundwater and why does it matter?

Young groundwater is groundwater that is less than 50 years old. It’s an arbitrary cutoff but it shows where groundwater has been recently renewed and will be renewed in the next 50 years. Old groundwater is often deeper and less accessible and often, but not always, has lower water quality. It can often be saline, even more salty than ocean water. … These things limit our ability to use this water for drinking water or for irrigating crops.

What was your most significant finding?

The biggest finding we have is that less than six per cent of groundwater globally is renewable on this human lifespan timescale, so over 50 years. Yet, and this is kind of the interesting thing, this modern or young groundwater is actually three times larger than the volume of all the other freshwater in the Earth.

What does this finding say to you?

The biggest implication is that these young groundwater resources are a finite resource that we need to protect and manage better. They’re important because they’re the most quickly renewed, yet they’re also the most vulnerable or sensitive to both contamination from the surface and to climate change.

Do you have a sense of where we’re over-using groundwater?

Previous studies that myself and other people have done have documented where we’re over-using ground water. Some of those places include northern India, northern China, Saudi Arabia, and in the United States, in the midwest, such as Kansas, Texas, and most recently in the news, in California.

Does your study have any implications for Canada or B.C.?

B.C. has just recently passed a new Water Sustainability Act, which for the first time really regulates groundwater use in this province. Our groundwater studies are really important to show and to try to estimate how much groundwater we have and where we have it, and that can be used for how to better manage it. This is true across Canada. B.C. has just been a little bit behind the times, and now we’re finally catching up to in developing groundwater regulations.

Do you hope your study has an impact on policy-makers?

I hope it’s a call and a reminder that our young and active groundwater is a finite resource that needs to be managed and protected into the future.