Sewage Waters a Tenth of World's Irrigated Crops

Fred Pearce New Scientist

The agricultural debate in the United States often revolves around whether produce is -- or should be -- organic, conventionally grown, or genetically modified. In countries such as India, Pakistan, and Sri Lanka, though, the most pressing question is whether or not crops have been irrigated by untreated sewage, which is illegal and poses serious heath risks to both farmers and consumers.

Government agencies in these countries are aware of the problem, but tend to look the other way because untreated sewage is cheap and easy. Farmers like the nitrogen- and phosphate-rich effluent, because it acts as a fertilizer and is free of charge. And unlike water in local irrigation canals, it flows even during droughts and dry seasons.

'Wastewater irrigation is an institutional no man's land,' said Chris Scott of the Sri Lanka-based International Water Management Institute. 'Water, health and agriculture ministries in many countries refuse to recognize that the practice is widespread.'

A survey co-edited by Scott's organization and presented at the Stockholm Water Symposium estimates that one-tenth of the world's crops are irrigated with sewage, much of it raw and untreated. The problem is particularly acute in developing nations, where farms that yield nearly one-fifth of the world's food supply are in either in, or on the fringes of a large, congested city , where freshwater is scarce. In Hyderabad, India, for instance, the survey estimates that 100% of the urban crops are irrigated by some sort of sewage.

Raw sewage is full of disease-carrying pathogens and toxic industrial waste, but if it were treated properly it could be used for irrigation. In Mexico, Jordan, Israel, and Tunisia, for example, sewage is specially treated to remove pathogens and make it safe for irrigation.
-- Elizabeth Dwoskin