Scores of cities using untreated wastewater

Cities in developing countries around the world are using untreated or partially treated wastewater for agriculture, posing serious health risks to urban consumers, according to a study.

"Irrigating with wastewater isn't a rare practice limited to a few of the poorest countries," said researcher Liqa Raschid-Sally, a researcher for the International Water Management Institute (IWMI).

"It's a widespread phenomenon, occurring on 20 million 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."

The IWMI said wastewater was most commonly used to produce vegetables and cereals, especially rice.

The study looked at 53 cities in Latin America, the Middle East, Africa and Asia. In a report released to coincide with an annual water conference in Sweden, it found 80 per cent were using untreated or partially treated wastewater.

"In over 70 per cent of the cities studied, more than half of urban agricultural land is irrigated with wastewater that is either raw or diluted in streams," the institute said.

At the same time, the IWMI noted that wastewater agriculture contributes to urban food supplies and helps provide a livelihood for the urban poor.

The institute highlighted Accra, Ghana's capital city, as an illustration of the tradeoffs from wastewater-based agriculture.

Few developing countries reported having official guidelines for use of wastewater in agriculture and in the cases where they did exist there was little enforcement, the IWMI said.

The institute saw no quick fixes.

"In the face of water scarcity generally and a lack of access to clean water, urban farmers will have no alternative except to use diluted or untreated wastewater or polluted river water," it said.

One option is to build on local practices. In Indonesia, Nepal, Ghana and Vietnam, for example, farmers store wastewater in ponds to allow suspended solids to settle.