The amount of farmland irrigated with untreated wastewater is much greater than previously thought, new research suggests.
The findings of a study published in Environmental Research Letters have serious implications for the health of city dwellers in developing countries.
The study used geographic information systems-based modelling methods to develop the first spatially-explicit estimate of the global extent of irrigated croplands influenced by urban wastewater flows, including both direct and indirect wastewater use.
It found that the area affected by untreated wastewater is around 30 million hectares, a 50 per cent increase on the previous estimate.
It also found that 65 per cent of downstream irrigated croplands were within 40 km of an urban area, with high levels of dependence on wastewater flows. Most of these croplands were in around 70 countries with low levels of wastewater treatment, exposing 885 million urban consumers as well as farmers and food vendors to serious health risks. Five countries – China, India, Pakistan, Mexico and Iran – account for most of this cropland.
These figures provide an insight into the key role that wastewater plays in meeting the water and food needs of people around the world, as well as the need to invest in both wastewater treatment and in safer practices to protect environmental and public health.
“We've not just looked at wastewater, we've also looked at the wastewater that enters the rivers and streams, where it gets diluted to some extent but it is still tremendously dangerous when it comes to farmers' fields,” study co-author Pay Drechsel from the International Water Management Institute told the BBC.
Health risks to consumers can be reduced through safer irrigation and greater hygiene at markets. “Also people can effectively wash the vegetables so you can get rid of most of the pathogens, but in those countries where it is most needed, there is no risk awareness. People don't know about bacteria,” said Drechsel.
Wastewater, if properly treated, is a great opportunity, but we need to find ways of using it without risking food safety.
“Wastewater is an asset if the right policies, technologies and financial incentives are in place. But at the same time awareness needs to be raised among those dealing with wastewater reuse to prevent illness and maximize benefits,” says Birguy Lamizana, a UN Environment water resources management expert.
Polluted irrigation canal in Changua County, Taiwan ©:Changua Coast Conservation
“Wastewater discharge heavily impacts both people and our water bodies. We estimate that severe pathogenic pollution – primarily from a lack of sanitation treatment – can be found in up to a third of rivers in developing countries, leading to direct health effects.”
Wastewater will be in focus at this year’s World Water Week – an annual gathering focusing on the globe’s water issues. The theme for the 28 August – 2 September event in Stockholm is “Water and Waste – Reduce and reuse”. The week aims to provide an opportunity for practitioners, policy makers and the public to brainstorm practical solutions to the world’s water challenges.
Read our recent story Wastewater challenges – and opportunities.
Read IRIN’s 2012 story Sewage-fed vegetables give pause for thought
The UN Environment Assembly, the world's highest-level decision-making body on the environment, will gather in Nairobi, Kenya, from 4-6 December 2017 under the overarching theme of pollution.
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For more information on the work UN Environment is doing on water quality, freshwater ecosystem health, wastewater and water pollution: Birguy.lamizana[at]unep.org and Elisabeth.Bernhardt[at]unep.org
