Groundwater represents around 35% of water distributed for potable supply in England and Wales and is also utilized by industry and for private supplies. It is of high quality and requires little treatment before use. It is important, therefore, that a robust policy of groundwater protection is available to protect the resource from pollution, as rehabilitation of polluted groundwater is expensive, and often may not be technically feasible. One way to protect aquifers is to control activities which pose a threat to groundwater quality, especially in areas where they are naturally poorly protected. Areas where groundwater is at risk of pollution from surface activities are indicated on maps by characterizing the properties of the underlying soils and rocks. The rocks are classified on the basis of their permeability, into Major, Minor and Non-Aquifers. The soils overlying aquifers are then categorized on their physical and chemical properties into leaching potential classes. The Groundwater Protection Policy of the Environment Agency, of which the groundwater vulnerability maps are part, provides guidance on those types of development which require controlling if groundwater quality is to be maintained in the long term. The relevance of these maps to other environmental issues is discussed.