<i>Dry Africa sits on 'huge' water resource </i>
The notoriously dry continent of Africa is sitting on a vast reservoir of groundwater, say scientists.
They argue that the total volume of water in aquifers underground is 100 times the amount found on the surface.
The team have produced the most detailed map yet of the scale and potential of this hidden resource.
Due to changes in climate that have turned the Sahara into a desert over centuries many of the aquifers underneath were last filled with water over 5,000 years ago.
The scientists collated their information from existing hydro-geological maps from national governments as well as 283 aquifer studies.
The researchers say their new maps indicate that many countries currently designated as "water scarce" have substantial groundwater reserves.
Across Africa more than 300 million people are said not to have access to safe drinking water.
Demand for water is set to grow markedly in coming decades due to population growth and the need for irrigation to grow crops.
Freshwater rivers and lakes are subject to seasonal floods and droughts that can limit their availability for people and for agriculture. At present only 5% of arable land is irrigated.
Now scientists have for the first time been able to carry out a continent-wide analysis of the water that is hidden under the surface in aquifers. Researchers from the British Geological Survey and University College London (UCL) have mapped in detail the amount and potential yield of this groundwater resource across the continent.
However, the scientists are cautious about the best way of accessing these hidden resources. They suggest that widespread drilling of large boreholes might not work.