Millions of slum residents across the world suffer the hazards and misery of frequent flooding of their streets and homes, which may result in savings of a lifetime being washed away in a few hours, damaged property, loss of work and time, and higher risks of diarrhoea, worm infection and other health problems. This manual is written to help engineers, aid and agency workers understand drainage problems more clearly in the developing world, so that they can work towards finding practical solutions. It focuses on three questions of particular relevance to low-income urban areas in developing countries: what is drainage performance? how can we evaluate a drainage system, to access how best to improve its performance? what are the effects of solids in drains upon performance? This manual is the outcome of two-and-a-half years of fieldwork in the city of Indore, in Madhya Pradesh, India and can be used as a practical aid by municipal engineers, consulting engineers and engineering instructors and students, as well as development and aid workers involved in drainage systems.