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When urban areas expand without concomitant increases in wastewater treatment capacity, vast of wastewater are released to surface waters with little or no treatment. Downstream of many areas are large areas of irrigated croplands reliant on these same surface water sources. Case studies the widespread use of untreated wastewater in irrigated agriculture, but due to the practical and challenges of conducting a true census of this practice, its global extent is not well known except reuse has been planned. This study used GIS-based modeling methods to develop the first spatially estimate of the global extent of irrigated croplands influenced by urban wastewater flows, including wastewater use. These croplands were further classified by their likelihood of using poor quality based on the spatial proximity of croplands to urban areas, urban wastewater return flow ratios, and of wastewater treated. This study found that 65 percent (35. 9 Mha) of downstream irrigated were located in catchments with high levels of dependence on urban wastewater flows. These catchments were home to 1. 37 billion urban residents. Of these croplands, 29. 3 Mha were located in with low levels of wastewater treatment and home to 885 million urban residents. These figures insight into the key role that water reuse plays in meeting the water and food needs of people the world, and the need to invest in wastewater treatment to protect public health.
Thebo et al. (Sat,) studied this question.