A third of the world's population will be short of fresh water by the year 2025, according to the report just published by the Johns Hopkins Population Information Programme in the United States.

With prompt action, says the report, water shortages can be avoided, but without action, water wars are set to be a feature of the next century.

Water loss could be reduced by up to 90%

The worst water shortages are expected in the developing world, where a combination of rapid population growth, pollution and inefficient use of water already puts a huge strain on water resources.

The programme calls for urgent action - a "Blue Revolution" to conserve and manage fresh water supplies by combining the use of water handling technology with international water sharing agreements.

Technologies have been developed that can reduce water loss by up to 90% and these should be implemented in countries that can afford the large investments required.

Elsewhere, the report argues, centuries-old water conservation techniques exist that can be used to similar effect.

The second half of the revolution requires countries to agree water sharing pacts, such as the agreement between India and Bangladesh to share the water of the Ganges river.