Wastewater is widely used to irrigate urban agricultural land in developing countries, a practice that has both advantages and disadvantages, a 53-city study presented at a water conference in Stockholm showed Monday.
Wastewater agriculture contributes importantly to urban food supplies and helps provide a livelihood for the poor, but can also lead to health risks for consumers, particularly for vegetables consumed uncooked, the report by the International Water Management Institute (IWMI) said.
Wastewater has a "large potential... for both helping and hurting great numbers of urban consumers," IWMI researcher Liqa Raschid-Sally said in a statement.
The survey showed that 80 percent of cities studied were using untreated or partially treated wastewater for agriculture. In over 70 percent of the cities studied, more than half of the urban agricultural land was irrigated with wastewater.
Wastewater was being used primarily to produce vegetables and rice.
The practice was being used on 20 million hectares (almost 50 million acres) 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," the statement said.
In Ghana's capital Accra, for example, which has almost two million inhabitants, some 200,000 city residents purchase vegetables each day produced on just 100 hectares of urban agricultural land irrigated with wastewater, the report said.
The report did not call for a ban on the use of wastewater, saying such a move could "adversely affect urban consumers, farmers and others who depend on urban agriculture."
Instead, it urged local authorities to develop policies for safer wastewater use, and advocated low-cost measures such as the use of drip irrigation, correct washing of produce, and wastewater storage ponds to allow suspended solids to settle out.
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