More than half of humanity will be living with water shortages, depleted fisheries and polluted coastlines within 50 years because of a worldwide water crisis, warns a United Nations report out Monday.

Waste and inadequate management of water are the main culprits behind growing problems, particularly in poverty-ridden regions, says the study, the most comprehensive of its kind. The United Nations Environment Programme, working with more than 200 water resource experts worldwide, produced the report.

Tens of millions of people don't have access to safe water. It is indeed a crisis,

In developed nations such as Japan, the USA and in Europe, most water shortfalls arise from politically popular but inefficient subsidies and protections of agriculture, which accounts for 85% of freshwater consumption worldwide.

Developing regions don't need more dam-building projects, he says, but need more people trained to manage water systems.