This strategy features in the framework of Agenda 21 as formulated at UNCED (Rio de Janeiro, 1992), now coordinated by the United Nations Commission on Sustainable Development and implemented through national and local authorities. Agenda 21 recommends study of the key processes in water-quality genesis using research models built on hydrological balance studies and including the consumptive use of water. This approach should also, when appropriate, be applied at the catchment level.