Agricultural methods need to be radically overhauled to ensure food production rises to meet increasing demand but that water resources are not depleted further by doing so, research showed on Monday.

A radical overhaul of agriculture could create farms that enhance, rather than degrade, the world's ecosystems, said a report led by the United Nations' Environment Programme and the International Water Management Institute (IWMI).

"Managing water for food and ecosystems will bring great benefits, but there is no escaping the urgency of the situation," said David Molden, deputy director general for research at IWMI.

"We are heading for disaster if we don't change our practices from business as usual," he added.

Water limits are close to being "reached or being breached" in areas such as northern China, India's Punjab and western United States, said the report, entitled 'An Ecosystem Services Approach to Water and Food Security'.

It warns that the number of people living in conditions of water scarcity could rise to 2 billion from 1.6 billion if the intensification of agriculture is not changed.

"People underestimate the amount of water used to make food. An average 2,000-3,000 litres per day is needed to produce food per person, compared to 200-300 litres for household use per day," Molden told Reuters.

"On a global scale, we are likely to produce (enough) food but that doesn't solve the environmental problems and locally, we are already seeing the crunch."

The world's population is forecast to rise to over 9 billion by 2050 from its current 6.9 billion, putting more strain on resources.

"We need to double food production if population goes up by a third, because people eat more meat and vegetables. And if we don't change water practices, we need to find 70 percent more water," Molden said.

To achieve both food and environmental security, governments need to provide incentives to farmers to adopt more sustainable agricultural practices, he added.

Farmers need to think about their business as more than just food production, while consumers need to demand good agricultural methods.

There are many opportunities to use trees on dry-land farms to intensify the amount of food produced per hectare of land while improving the local ecosystem, the report found.

By integrating trees and hedgerows, farmers can prevent runoff and soil erosion and preserve more water for feeding their crops.

Last month, a separate U.N. report said a sharp move away from large-scale, intensive systems of agriculture was essential if growing environmental and land degradation was to be halted.