Estimating the leakage contribution of phosphate dosed drinking water to environmental phosphorus pollution at the national-scale

Understanding sources of phosphorus (P) to the environment is critical for the management of freshwater and marine ecosystems. Phosphate is added at water treatment works for a variety of reasons: to reduce pipe corrosion, to lower dissolved lead and copper concentrations at customer's taps and to reduce the formation of iron and manganese precipitates which can lead to deterioration in the aesthetic quality of water. However, the spatial distribution of leakage into the environment of phosphate added to mains water for plumbosolvency control has not been quantified to date. Using water company leakage rates, leak susceptibility and road network mapping, we quantify the total flux of P from leaking water mains in England and Wales at a 1km grid scale. This is validated against reported leaks for the UKs largest water utility. For 2014, we estimate the total flux of P from leaking mains to the environment to be c. 1.2ktP/year. Spatially, P flux is concentrated in urban areas where pipe density is highest, with major cities acting as a significant source of P (e.g. London into the Thames, with potentially 30% of total flux). The model suggests the majority (69%) of the P flux is likely to be to surface water. This is due to leakage susceptibility being a function of soil corrosivity and shrink–swell behaviour which are both controlled by presence of low-permeability clays. The location of major cities such as London close to the coast results in a potentially significant flux of P from mains leakage to estuarine environments. The contribution of leakage of phosphate dosed mains water should be considered in future source apportionment and ecosystem management. The methodology presented is generic and can be applied in other countries where phosphate dosing is undertaken or used prior to dosing during investment planning. Images copyright of Oliver Dixon (http://www.geograph.org.uk/reuse.php?id=2139075), Horst Gutmann (https://www.flickr.com/photos/zerok/2389209453) and N Chadwick (http://www.geograph.org.uk/photo/3223601). Images are licensed under the Creative Commons Attribution-Share Alike 2.0 Generic Licence (http://creativecommons.org/licenses/by-sa/2.0/). [Display omitted] •The national scale P flux from leaking water mains to the environment is quantified.•We estimate the annual flux to be 1.2ktP/year.•69% of the flux is to surface water due to high leakage susceptibility on non-aquifers.•Urban areas may be a significant contributor to P flux due to h