Nearly 30 million hectares of cropland worldwide is likely to be irrigated with untreated wastewater – 50% more than previously estimated, a study reveals.
Vital infrastructure, including wastewater treatment plants, is failing to keep pace with population growth; more than 80% of wastewater produced globally enters the environment without treatment.
For farmers, although it is dangerous, untreated wastewater also has benefits. It provides a reliable source of water for irrigating crops, and it has a higher concentration of nutrients than other water sources.
Many of those crops are consumed as street food by around 800,000 people, but studies have shown that the crops are often teeming with E. coli bacteria. So, what is the global extent of this problem?
In addition, the scientists assessed indirect or de facto wastewater use, where wastewater enters rivers and streams and is used downstream.
The study, published in Environmental Research Letters (ERL), found that 65% of all irrigated croplands within 40 km downstream from urban areas – amounting to more than 35 million hectares – were in catchments with high levels of dependence on urban wastewater flows.
Thebo and her colleagues estimate that worldwide some 885 million urban residents are exposed to serious health risks as a result of routine irrigation with highly polluted water.
"To feed the growing population, wastewater irrigation is going to play an important role, but we need to improve safety," said Drechsel.