Wastewater 'widely used' in urban agriculture, report finds

Many of the major cities in developing countries are using untreated or partially treated wastewater to irrigate nearby farmland, according to the International Water Management Institute (IWMI).

In a report, released yesterday (18 August) at the World Water Week summit in Stockholm, Sweden, the IWMI highlights the need to develop practical measures in utilising wastewater while avoiding potential environmental and health risks.

Wastewater, mainly produced in cities, is directly used to solve the shortage of irrigation water in many developing countries. The IWMI says that wastewater irrigation occurs on around 20 million hectares of farmland across the developing world.

The authors of the report surveyed 53 cities across Africa, Asia, Latin America and the Middle East. They found that over 80 per cent of the cities studied used untreated or partially treated wastewater for agriculture.

Wastewater can contain high amounts of nutrition for crops, such as nitrogen and phosphorus, saving fertiliser costs for farmers. However, untreated water may also contain high amounts of organic pollutants or heavy metals, which can enter the food chain directly through irrigation.

But the authors do not recommend banning or reducing the practice by imposing stricter water criteria, since poor infrastructure and lack of funding in developing countries would hinder such measures and adversely affect farmers dependent on wastewater.

Instead, they say that innovative indigenous practices can be built upon to help reduce the health risks from wastewater agriculture. For example, in Ghana, Indonesia, Nepal and Vietnam, farmers store wastewater in ponds to allow suspended solids to settle out before use in irrigation.

The authors say the Millennium Development Goals (MDGs) on clean water should more closely link policies and investments for improvements in the water supply sector with those of the sanitation and waste disposal sector.

"The MDGs should rightly have a sanitation goal, but also mention safe disposal of water for productive and environmentally friendly reuse where feasible," David Molden, deputy director-general for research at the IWMI, told SciDev.Net.

Feng Shaoyuan, deputy director of China Agricultural Water Research Centre, says the report highlights the need for better policies to regulate wastewater farming.

"For example, wastewater irrigation should only be used for forest, grasslands and non-food crops. Also, wastewater irrigation should not be used near potable or clean water sources to avoid pollution," Feng told SciDev.Net.     

"With these policies, the health and environmental impacts of it can be greatly reduced even if there is insufficient infrastructure to treat wastewater,"