More than ninety per cent of the developed world live in cities, and developing countries are moving rapidly in the same direction. Urban aquifers are vitally important for water supply, but are at high risk of pollution and slow to cleanse themselves. This book explains the nature and value of urban groundwater. It discusses the types of pollutants that are found and their sources. A unique aspect of this book, written by a UNESCO/IAH group, is the in-depth discussion of six different urban environments ranging from mature industrial cities, through weathered crystalline aquifers to arid-zone cities.