The volume of sewage and industrial effluents in the world is set to rise in line with population growth. Furthermore, the growth in global wealth means our wastewater, including sewage, contains increasing amounts of dangerous chemicals, toxic substances and the debris associated with modern consumer lifestyles. Take the Ganga (Ganges) river in India, it supports a population of some 500 million people, roughly equal to the population of the United States, Russia and Canada combined, and provides water for cooking, bathing, irrigating crops and sustaining livelihoods. For many people it also has great spiritual and cultural value. Globally, unclean water poses significant risks of diseases like diarrhoea, opportunistic infections and malnutrition, accounting for 1.7 million deaths annually, of which over 90 per cent are in developing countries and almost half are children. These deaths are primarily due to ingestion of faecal pathogens from humans or animals and toxic metals.