A 53-city study study presented to a Stockholm conference today will say that waste water is being widely used to irrigate urban agricultural land in developing countries.

Researchers concluded that this practice has both advantages and disadvantages, a water conference in the Swedish capital was told. Waste-water agriculture contributes importantly to urban food supplies and helps provide a livelihood for the poor.

But the use of sewerage, to give the water its more widely used label, can also lead to health risks for consumers, particularly for vegetables consumed uncooked.

International Water Management Institute (IWMI) researcher Liqa Raschid-Sally said 80 per cent of cities studied were using untreated or partially treated waste water for agriculture. In over 70 per cent of the cities studied, more than half of the urban agricultural land was irrigated with waste water.

The water is being used primarily to produce vegetables and rice on approximately 20 million hectares of land, especially in Asian countries like China, India and Vietnam, but also "nearly every city of sub-Saharan Africa and in many Latin American cities as well," said an IWMI statement.

The report does not call for a ban on the use of waste water, but urges local authorities to develop policies for safer waste-water use, and advocates low-cost measures such as the use of drip irrigation, correct washing of produce, and waste-water storage ponds to allow suspended solids to settle out.

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