Adding soil data, including information about the underlying rock, may help to show the possible effects of fractured crystalline rock on water pollution, according to MacDonald and Karen Villholth, a groundwater researcher at the International Water Management Institute, based in South Africa.

Cracks in these rocks, which underlie about a third of African land, allow a greater amount of water to sink into underground reserves. This means that some areas in East and West Africa may be even more vulnerable to groundwater pollution than the map suggests, Villholth says.

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