Water is basic to a large number of values that are important to people. In addition to its direct and immediate life-supporting attributes, it is also essential for the continued functioning of most other ecosystems in the natural environment. The level of human impact on the natural world is now so great, however, that in many situations it has become necessary to deliberately set aside a proportion of the available water so that the environment and its ecosystems can continue to function. Water used for this purpose is described by the all embracing term 'environmental water'. However, as this discussion paper shows, that umbrella description includes a great variety of different strategies, aims and situations.