Global use of wastewater for agriculture at least 50 percent greater than thought
The study relies on advanced modeling methods to provide the first truly comprehensive estimate of the global extent to which farmers use urban wastewater on irrigated cropland.
Researchers analyzed data with geographic information systems (GIS) rather than depending on case study results, as in previous studies.
The researchers also assessed for the first time 'indirect reuse', which occurs when wastewater gets diluted but still remains a dominant component of surface water flows.
Such situations account for the majority of agricultural water reuse worldwide, but have been difficult to quantify on a global level due to different views of what constitutes diluted wastewater versus polluted water.
Considering consumer safety the foremost priority, study authors highlight the need to mitigate public health risks through measures taken along the entire food supply chain.
This includes improved wastewater treatment, but also preventive steps on farms and in food handling, since capacity for water treatment is increasing only slowly in developing countries.
According to the study, farmers' use of wastewater is most prevalent in regions where there is significant wastewater generation and water pollution.
In these circumstances, and where safer water is in short supply, wastewater offers a consistent and reliable means of irrigating fields, including high-value crops, such as vegetables, which often require more water than staple foods.
Where raw wastewater is available, farmers may tend to prefer it because of its high concentrations of nutrients, which can lessen the need to apply purchased fertilizers.
In most cases, however, farmers' use of this water is motivated by basic needs; they simply do not have alternatives. ■