Study of 53 cities across the world finds 'widespread' use of waste water contaminated with heavy metals and sewage

At least 200 million people around the world risk their health daily by eating food grown using untreated waste water, some of which may be contaminated with heavy metals and raw sewage, according to major study of 53 world cities.

Urban farmers in 80% of the cities surveyed were found to be using untreated waste water, but the study said they also provided vital food for burgeoning cities at a time of unprecedented water scarcity and the worst food crisis in 30 years.

The study from the UN-backed International Water Management Institute (IMWI), said the practice of using waste water to grow food in urban areas was not confined to the poorest countries.

"It's a widespread phenomenon, occurring on 20m hectares across the developing world, especially in Asian countries like China, India and Vietnam, but also around nearly every city of sub-Saharan Africa and in many Latin American cities as well," said IWMI researcher Liqa Raschid-Sally.

"Nor is it limited to the countries and cities with the lowest GDP. It is prevalent in many mid-income countries as well", she said.

The report, launched today at World Water Week in Stockholm, Sweden, found the practice "widespread and practically inevitable".

"As long as developing countries lack suitable transport to deliver large quantities of perishable produce to urban areas, urban agriculture will remain important. In the face of water scarcity generally and a lack of access to clean water, urban farmers will have no alternative except to use … polluted water", write the authors.

The report found that few developing countries have official guidelines for the use of waste water in agriculture. Even if they do, monitoring and enforcement rarely happen and may not be realistic. As a result, though the practice may be theoretically forbidden or controlled, it is "unofficially tolerated."

Earlier in 2008, the UN's World Health Organization stated that a global environmental and health crisis was unfolding with more than 200m tonnes of human waste a year being dumped untreated in water systems, exposing hundreds of millions of people to disease.

The International Union for Conservation of Nature (IUCN), said on Sunday that rivers around the world are now seriously polluted "to the brink of collapse".

"Many rivers in developing countries and emerging economies are now polluted to the brink of collapse. For example, the Yangtze, China's longest river, is suffering because of pollution by untreated waste, agricultural run-off and industrial discharge", said a spokesman.