Mains water leakage: Implications for phosphorus source apportionment and policy responses in catchments

•Mains water leakage of phosphate (MWL-P) dosed drinking water is currently not included in P budgets•A new approach to estimate the spatial distribution and time-variant flux of MWL-P is demonstrated in an exemplar catchment•Measures to reduce P from agricultural and sewage mean MWL-P could become a relatively more significant source of P•There is a need to balance human health with ecological health•New research is needed to better constrain the ultimate fate of MWL-P and the role of MWL-P within aquatic ecosystems

Effective strategies to reduce phosphorus (P)-enrichment of aquatic ecosystems require accurate quantification of the absolute and relative importance of individual sources of P. In this paper, we quantify the potential significance of a source of P that has been neglected to date. Phosphate dosing of raw water supplies to reduce lead and copper concentrations in drinking water is a common practice globally. However, mains water leakage (MWL) potentially leads to a direct input of P into the environment, bypassing wastewater treatment. We develop a new approach to estimate the spatial distribution and time-variant flux of MWL-P, demonstrating this approach for a 30-year period within the exemplar of the River Thames catchment in the UK. Our analyses suggest that MWL-P could be equivalent to up to c.24% of the P load entering the River Thames from sewage treatment works and up to c.16% of the riverine P load derived from agricultural non-point sources. We consider a range of policy responses that could reduce MWL-P loads to the environment, including incorporating the environmental damage costs associated with P in setting targets for MWL reduction, alongside inclusion of MWL-P within catchment-wide P permits.

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