This is a fascinating discovery which has recently come to light. Scientists estimate that Africa’s groundwater totals about 0.66 million cubic kilometers, which means the continent has over 100 times more water underground than on the surface. And huge amounts of that fossil water (estimated to be as much as a million years old in places) is underneath the Sahara. Don’t expect the desert to start becoming a major supplier of soft fruit any time soon (the ground water is over 250m deep for a start), but it is a very interesting (and academic) article. For those of you who prefer maps, this is the best one, as it shows the productivity of the aquifers and their depth in the same image.
Fossil water under the Sahara Desert – Africa – ech2o newsletter snippet