This book is based on concepts of water supply-related health risk assessment developed by the authors during the course of the Water Decade.These concepts would not have been worth publishing without the practical support provided by several hundred sanitary officers, scientists, engineers, doctors and close colleagues. They have provided the essential information, largely con-tained in pilot project reports, which have confirmed that a systematic approach to surveillance and risk assessment provides the necessary basis on which to improve and maintain the safety of community water supplies.