Researchers calculated relative volumes across the globe of so-called modern groundwater, which accumulated in underground reservoirs in the past half century. The above map showing the calculated volumes indicates how deep the groundwater would be if it were pooled directly above the ground under which it resides. The scientists lacked data from areas, shown in white, where permafrost is widespread. Credit: Tom Gleeson, Kevin M. Befus, Scott Jasechko, Elco Luijendijk and M. Bayani Cardena (2015). Nature Geoscience, DOI:10.1038/NGEO2590