Acknowledgements

This research was performed as part of an interdisciplinary project programme ‘Clean water for all’, undertaken by the Blue-Green Cities Research Consortium (www.bluegreencities.ac.uk) and the Portland–Vancouver urban long-term research area (Ultra) project. The consortium is funded by the UK Engineering and Physical Sciences Research Council under grant EP/K013661/1, with additional contributions from the Environment Agency and Rivers Agency (Northern Ireland). Ultra is funded by the United States National Science Foundation under grant 0948983.