1. a Grantham Research Institute for Climate Change, London School of Economics, London WC2A 3PH, UK
2. b FundiFix Water Services Trust, Kyuso Centre, Kitui, Kenya
3. c School of Geography and the Environment, University of Oxford, South Parks Rd, Oxford OX1 3QY, UK
4. d Department of Engineering Science, University of Oxford, Headington, Oxford OX3 7DQ, UK