A water basin is a natural unit for both land and water management, as most of the interactions and impacts of land and water use are restricted to within basin boundaries. Land and water use in one part of a water basin can impact on other parts of the basin, but generally not outside the basin. (River borne pollution flowing into the ocean being the main exception). While this primarily applies to physical interactions, economic and social factors also reflect water basin boundaries, to varying degrees.

"The watershed as a landscape-level unit becomes an ideal management focus because it is both a geographic unit, usually with discrete boundaries, and a functional system unit with inputs and outputs." (D. P. Odum, Institute of Ecology, University of Georgia, Athens, Georgia in: Watershed Management: Practices, Policies and Co-ordination. R. J. Reimold, Editor McGraw-Hill.1998).

"River basins are often economic regions, too. Patterns of settlement, agriculture and transportation along rivers have tended to integrate the economies, linking basic industries (agriculture, livestock, mining, forestry) with secondary and service industries. Thus, the main economic and demographic effects of water projects and policies are likely to occur right in the same river basin." (Howe, C. Guidelines for the Design of Effective Water Management Institutions Utilizing Economic Instruments. Paper presented at UNEP Workshop on the Use of Economic Principles for the Integrated Management of Freshwater Resources, Nairobi, June 1995).

"The watershed has been a compelling integrating concept in ecological and geological sciences (Hornbeck and Swank, 1992). Hydrological catchments have been used to understand the water cycle, geomorphologic dynamics, soil formation, and other processes (Band et al., 1993). They have also been used to understand water yield and quality, interactions between terrestrial and aquatic systems, biomagnification, and successional relationships. They have been employed as powerful comparative and experimental tools that have contributed to basic scientific understanding and the solution of key practical problems (Hedin and Campos, 1991). The recognition of and approach to non-point source pollution and to acid deposition are examples of the practical application of watersheds (Likens et. al., 1996), and exemplify the power of the watershed experimental approach (Golley, 1993) even in open systems. Another practical benefit is that the watershed perspective ensures that key functional aspects of metropolitan areas - hydrology and wetlands - are not neglected in cities and suburbs." … "Finally, the watershed approach can be used to link contrasting catchments with estuaries and coastal waters. Because of the great significance of non-point source pollution, understanding the role of catchments of various sizes and degrees and kinds of human use becomes crucial (Costanza and Greer, 1995)." (S.T.A. Pickett, W.R. Burch, Jr., S.E. Dalton, T.W. Foresman, J.M. Grove, R. Rowntree, A conceptual framework for the study of human ecosystems in urban areas. Urban Ecosystems, 1997,1, 185-199).