The spectacular industrial and economic development of the twentieth century was  achieved at a considerable environmental cost. The increasingly precarious position of water, the most valuable of natural resources, reflects this trend. Today we have come to realise that concepts of sustainable development need to replace the antiquated belief that the environment in general, and natural resources in particular, are simply there for the taking. The responsible use of water, in which man profits from resources without endangering their future, should have precedence in any water policy. Regional Water System Management contains invited lectures presented by eminent authors to the international Seminar Regional Water Management. Water Conservation, Water Supply, Systems Integration held in Valencia (Spain) in 2002. The publication provides a general overview of  basic water management principles for the twenty-first century and will be of interest to those studying water conservation, as well as professionals already in the field.