By Grant Ferret
BBC Africa editor
Scientists and researchers meeting in the Kenyan capital, Nairobi, have warned of the growing threat posed by water shortages across Africa.
Hundreds of millions of people will be affected by drought
They say that in little more than 20 years' time, the number of people without access to clean water could double to over 600 million.
This would force the continent into an ever greater reliance on food aid.
The scientists say the shortages in Africa are part of a global trend of increasing water consumption.
The scientists from the Consultative Group on International Agricultural Research said shortages must be addressed at all levels - from the way farmers use water to international policy.
They say that if present trends continue, one third of the world's population will have insufficient water by the year 2025.
But it is in sub-Saharan Africa that the problem is worst.
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Already afflicted by periodic droughts, the researchers suggest the region will suffer more widespread shortages as the population grows.
They predict a shortfall in crop yields of over 20% because of insufficient water, with many governments too poor to finance the food imports needed to make up the difference.
To tackle the problem, the scientists are hoping to carry out a long-term programme to develop new breeds of high-yield crops which require less water.
But another of their suggestions is to put pressure on Western governments through the World Trade Organisation.
They say that agricultural subsidies in North America and Europe determine where food is grown, and that decisions taken by the WTO are possibly the single most important factor in shaping global demand for food and, as a consequence, the amount of water required to produce it.