After practicing international corporate law for 20 years, I returned to school and obtained an MSc in control of infectious diseases and a PhD in environmental health from the London School of Hygiene and Tropical Medicine. I joined the faculty of the LSHTM in 2004, and became Professor of Water, Sanitation and Health. I moved to the Rollins School of Public Health in 2013 as Professor of Environmental Health and Rose Salamone Gangarosa Chair of Sanitation and Safe Water. I lead a group of researchers whose work consists mainly of health impact evaluations of water, sanitation and household air pollution interventions in low-income countries. Publications include more than 15 RCTs in Latin America, Africa and South Asia; Cochrane reviews of water quality and sanitation interventions to prevent diarrhoeal disease and enteric infection; methods papers on improving the rigor of evalutating environmental health interventions; cost and cost-effectiveness analyses; and policy analyses of global environmental health initiatives. Current field research includes an evaluation of a rural water and sanitation programmes in Orissa; an RCT to assess the impact of arsenic water filters in West Bengal; a health impact evaluation of a large-scale deployment of water filters and improved cook-stoves in Western Province, Rwanda; and a trial to evaluate household air filters in New Delhi. I serve as an advisor to the World Health Organization in developing the first set of Guidelines on Sanitation and Health.