The protection of water quality at its source — the watershed — recognizes that minimizing land use impacts and allowing natural processes to provide in situ biological treatment can complement conventional engineering methods. In contrast to the enormous costs projected for drinking water filtration, the judicious application of watershed management principles and practices is a way to balance the needs of people with the capacity of the natural resource base over time. This paper describes the development and initial application of a geographic information system (GIS) to a ortion of New York City\u27s 2,000 square mile water supply system, the Esopus Creek watershed in the Catskill Mountains. Primary GIS layers depict topography, soils, vegetative cover, and land use. Secondary and derivative layers help to identify the primary streamflow and sediment source areas within the watershed. Although this method is a static representation of the landscape, it can serve as a guide to field inspections and related research to prioritize land for a conservation easement or protection program or to locate unstable areas in urgent need of restoration. Subsequent research includes the influence of contributing area, flow path, and soil properties on the travel time of subsurface flow
