From UNESCO: Groundwater Resources of the World

From the UNESCO press release:

Despite its strategic importance, no global inventory of this resource had been compiled to date. Since 2000, UNESCO’s International Hydrological Programme (IHP) has been participating in the establishment of a groundwater database. It is now presenting a detailed map of transboundary aquifers – available online – showing the delineations of aquifers that are shared by at least two countries. It also provides information about the quality of their water and rate of replenishment. So far, the inventory comprises 273 shared aquifers: 68 are on the American continent, 38 in Africa, 65 in eastern Europe, 90 in western Europe and 12 in Asia.

The aquifers, which contain 100 times the volume of fresh water that is to be found on the Earth’s surface, already supply a sizeable proportion of our needs.

Although aquifer systems exist in all continents, not all of them are renewable. For example, those in north Africa and the Arabian peninsula were formed more than 10,000 years ago when the climate was more humid and are no longer replenished. In some regions, even if the aquifers are renewable – being fed on a regular basis by rainfall – they are in some cases endangered by over-exploitation or pollution. In the small islands and coastal zones of the Mediterranean, populations often use groundwater more rapidly than it is replenished.

HT: The Map Room

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