New Global Groundwater Map
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 was 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, and was published in Nature Geoscience.
Measured groundwater ages range from months to millions of years. The study estimates global volume and distribution of groundwater less than 50 years old — "modern groundwater" — through a combination of geochemical, geologic, hydrologic, and geospatial data sets with numerical simulations of groundwater and tritium age analyses.
The research shows that less than 6% of groundwater in the upper 2 km of the Earth's landmass is renewable within a human lifetime. The total groundwater volume in the upper 2 km of continental crust is approximately 22.6 million km3, which represents a small percentage of the total groundwater on Earth yet dwarfs all other components of the active hydrologic cycle. The volume is equivalent to a body of water with a depth of about 3 m spread over the continents.
Get the paper here: http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2590.html