Africa's water systems need annual investments of about $20bn over the next two decades, a United Nations report has concluded.
The African Development Bank (ADB) says that only 3.8% of the continent's water resources are developed.
About 300 million Africans lack access to safe drinking water, and the ADB says money also needs to be spent on irrigation and hydropower.
The report was presented at the World Water Forum in Mexico.
It calls for an improvement in governance, as well as finance.
"Transparent, open, accountable, gender-responsive, communicative and effective water governance at all levels of water management is needed," said Kordjé Bedoumra, director of the ADB's African Water Facility.
At the opening of the Forum, the UN said that failed policies are the main reason why about 20% of the world's population lacks access to clean water.
Water power
The ADB says only about 3% of Africa's hydropower potential is tapped.
Observers are divided as to the best way of expanding hydropower, with some urging the construction of major new dams on grounds of efficiency while others promote smaller, community-level installations for social and environmental reasons.
The ADB's figure for farming is not much higher, with only about 6% of Africa's cultivated land under irrigation.
Across all sectors, demand for water is increasing, by around 3% per year in southern Africa.
And over most of the continent, rainfall is projected to decrease over the coming decades, a consequence of global climatic change.
But UN figures show investment in water infrastructure is falling, as governments struggle to provide adequate health care and education facilities.
Yet water and sanitation facilities are a key ingredient of social and economic progress.
At the World Water Forum, the ADB, together with the UN's human settlements agency UN-Habitat, announced a $550m loan programme aimed at developing small-scale drinking water projects in urban areas.
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