Following the water: Investigating de facto wastewater reuse in the Netherlands
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De facto wastewater reuse is the practice of extracting from surface water bodies which are impacted by treated wastewater (TWW) for the purposes of agricultural irrigation, managed aquifer recharge or drinking water supply. This process may be responsible for the propagation of TWW related contaminants through the hydrological system but may conversely represent a valuable way of accessing fresh water. The extent to which surface water bodies in the Netherlands are impacted by TWW is poorly understood, and the distribution of de facto reuse even more so. This study aims to address these knowledge gaps, with a focus on de facto reuse through agricultural irrigation. This is achieved via a novel application of the Water Framework Directive (WFD)-Explorer water quality model paired with a spatial analysis step, allowing for the distribution of different flow components – namely TWW and flow from transboundary rivers – to be discerned for the national surface water network. When paired with data on surface water extractions for irrigation, this identifies notable areas of de facto reuse. Results show that during dry conditions, TWW is a significant flow component in many surface water bodies, particularly in smaller water bodies located close to WWTPs. De facto reuse is indicated as widespread, with several areas in which extractions make use of water from impacted surface water bodies. This study represents a first attempt to directly link TWW emissions to agricultural irrigation, highlighting a mechanism by which wastewater associated contaminants can propagate through the hydrological system. It is likely to be useful for water managers in assessing sources of water quality issues and better regulating de facto reuse.