Watersheds are nature's boundaries for surface water supplies. Natural processes and human activities in watersheds combine to determine the inherent quality of these supplies and the treatment that they need for potable use. The quality of the drinking water at a consumer's tap depends on the source of that water and, in turn, on the approaches used in managing the activities and processes in the watershed from which the water originates. The effectiveness of these approaches depends to a significant extent on their scientific underpinnings. This seminar examines watershed management for the water supply of the City of New York. A central issue for New York City and, indeed, for all surface water supply systems, is this: how to develop and implement a watershed management strategy that safeguards the health of the citizens of the City while at the same time protecting the rights and economic well-being of the citizens residing in the watershed.