The UN World Water Development Report says almost 20 percent of the world's population lacks access to safe drinking water due to failed policies, a lack of resources and environmental problems.

These findings will be outlined next week at the World Water Forum in Mexico.

The report says politicians, businesses and aid charities all had a role in addressing the problem.

It says more still needs to be done, despite a streak of steady progress in recent years.

Unesco, which led the group of 24 UN agencies that put the data together, says the report highlights the need for stronger leadership and coordination.

Director general, Koichiro Matsuura, says, "Good governance is essential for managing our increasingly stretched supplies of freshwater, and indispensable for tackling poverty. There is no one blueprint... but we know it must include adequate institutions - nationally, regionally and locally - strong effective legal frameworks and sufficient human and financial resources."