An assessment from the U.N. Environment Program and the U.N. Human Settlements Program found that 40 percent of the 1 billion people in Africa live in locations without adequate sanitation or water supplies.
The number of African people living in urban areas without access to safe drinking water jumped from 30 million in 1990 to more than 55 million in 2008, UNEP added.
UNEP Executive Director Achim Steiner said the global push for a green economy could help allay some water and sanitation concerns.
"Indeed, public policies that redirect over a 10th of a percent of global gross domestic product per year can assist in not only addressing the sanitation challenge but conserve freshwater by reducing water demand by a fifth over the coming decades compared to projected trends," he said in a statement.
The joint report from the U.N. agencies on water and sanitation stress said urbanization in Africa is occurring faster than anywhere else in the world.