The world's governments agreed at the Millennium Summit to halve the number of people who lack access to safe water, by 2015. With rapidly growing urban populations, the challenge is immense. This report describes the impacts sanitations problems on health and economic performance, showing the potential gains of remedial action. It analyses the proximate and underlying causes of poor provision and identifies information gaps that affect resource allocation. It outlines the consequences of further deterioration and explains how resources and institutional capacities – public, private and community – can be used to deliver proper services through integrated water resources management.