LONDON, Nov 16 (Thomson Reuters Foundation) - 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. 
 
 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 www.trust.org) ||||| Groundwater: it's one of the planet's most exploited, most precious natural resources. It ranges in age from months to millions of years old. Around the world, there's increasing demand to know how much we have and how long before it's tapped out. 
 
 For the first time since a back-of-the-envelope calculation of the global volume of groundwater was attempted in the 1970s, an international group of hydrologists has produced the first data-driven estimate of the Earth's total supply of groundwater. The study, led by Dr. Tom Gleeson of the University of Victoria with co-authors at the University of Texas at Austin, the University of Calgary and the University of Göttingen, was published today in Nature Geoscience. 
 
 The bigger part of the study is the "modern" groundwater story. The report shows that less than six per cent of groundwater in the upper two kilometres of the Earth's landmass is renewable within a human lifetime. 
 
 "This has never been known before," says Gleeson. "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." 
 
 With the growing global demand for water--especially in light of climate change--this study provides important information to water managers and policy developers as well as scientists from fields such as hydrology, atmospheric science, geochemistry and oceanography to better manage groundwater resources in a sustainable way, he says. 
 
 Using multiple datasets (including data from close to a million watersheds), and more than 40,000 groundwater models, the study estimates a total volume of nearly 23 million cubic kilometres of total groundwater of which 0.35 million cubic kilometres is younger than 50 years old. 
 
 Why is it important to differentiate old from modern groundwater? Young and old groundwater are fundamentally different in how they interact with the rest of the water and climate cycles. Old groundwater is found deeper and is often used as a water resource for agriculture and industry. Sometimes it contains arsenic or uranium and is often more salty than ocean water. In some areas, the briny water is so old, isolated and stagnant it should be thought of as non-renewable, says Gleeson. 
 
 The volume of modern groundwater dwarfs all other components of the active water cycle and is a more renewable resource but, because it's closer to surface water and is faster-moving than old groundwater, it's also more vulnerable to climate change and contamination by human activities. 
 
 The study's maps show most modern groundwater in tropical and mountain regions. Some of the largest deposits are in the Amazon Basin, the Congo, Indonesia, and in North and Central America running along the Rockies and the western cordillera to the tip of South America. High northern latitudes are excluded from the data because satellite data doesn't accurately cover these latitudes. Regardless, this area is largely under permafrost with little groundwater. The least amount of modern groundwater is not surprisingly in more arid regions such as the Sahara. 
 
 "Intuitively, we expect drier areas to have less young groundwater and more humid areas to have more, but before this study, all we had was intuition. Now, we have a quantitative estimate that we compared to geochemical observations." says Dr. Kevin Befus, who conducted the groundwater simulations as part of his doctoral research at the University of Texas and is now a post-doctoral fellow at the United States Geological Survey. 
 
 The next step in painting a full picture of how quickly we're depleting both old and modern groundwater is to analyze volumes of groundwater in relation to how much is being used and depleted. 
 
 In a previous study that ultimately led to the investigation of modern groundwater, Gleeson's 2012 groundwater footprint report in Nature mapped global hot spots of groundwater stress, charting rates of precipitation compared to the rates of use through pumping, mostly for agriculture. Some of these hot spots are northern India and Pakistan, northern China, Iran, Saudi Arabia, and parts of the US and Mexico. 
 
 "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," says Gleeson. To do this, he will be leading a further study using a global scale model. 
 
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 Funding for this study came from Natural Sciences and Research Council, Canadian Institute for Advanced Research, US National Science Foundation and the American Geophysical Union. 
 
 The global volume and distribution of modern groundwater: http://nature. com/ articles/ doi:10. 1038/ ngeo2590 
 
 Note: This url will automatically redirect to the paper once it's published online (Nov. 16, 8 a.m. PST). 
 
 Modern groundwater map and photo of Dr. Tom Gleeson available for download at this DropBox link: http://ow. ly/ UuLdh 
 
 Media contacts: Tom Gleeson (Engineering) at 250-853-3934 or tgleeson@uvic.ca 
 
 Suzanne Ahearne (University Communications + Marketing) at 250-721-6139 or sahearne@uvic.ca 
 
 Follow us on Twitter: @uvicnews
– "We're using our groundwater resources too fast—faster than they're being renewed," Dr. Tom Gleeson says in a University of Victoria press release. Gleeson, along with fellow researchers, published the most accurate map of Earth's groundwater supply to date on Monday in Nature Geoscience. The study found there is about 14.3 million cubic miles of groundwater left on Earth. But that's not as encouraging as it sounds, according to Reuters, because no more than 6% of it is renewable within a human lifetime. "That's never been known before," says Gleeson, who adds that people are going to need to manage that resource better as water demands grow amid ongoing drought. "Groundwater can and should be thought of as a very useful buffer to climate extremes," he says. "It's a valuable and strategic resource for mitigating the extreme impacts of climate." The amount of groundwater less than 50 years old is enough to cover every continent with approximately 10 feet of water, according to the study. But while that young groundwater is more quickly replenished, it's also more easily polluted by people and impacted by climate change, Reuters reports. The rest of Earth's groundwater—which can be millions of years old—is much deeper underground and can be extremely salty and contain harmful elements, according to the press release. The next step is to figure out how dire the situation is. "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 says. (But at least we might have more helium left that we thought.)