Forests are critically important to the supply of clean drinking water in the Northeast and Midwest portion of the United States. In this part of the country more than 52 million people depend on surface water supplies that are protected in large part by forested lands. The public is generally unaware of the threats to their water supplies or the connection between clean water and the extent and condition of forest lands in source water watersheds. The future security of water supplies will not be ensured by a focus on water treatment alone. Protecting and managing forests in source watersheds is an essential part of future strategies for providing clean, safe drinking water that citizens can afford. This analysis uses a GIS-based process and a series of maps to create a watershed condition index based on physical and biological attributes. Using a multi-step process, this index is then used to compare 540 watersheds across 20 States and the District of Columbia, in terms of their ability to produce clean water. The study also quantifies the magnitude and scope of forest dependent drinking water supplies, and their dependence on private forests; and it identifies watersheds that are threatened by land use change or are in need of management to sustain and improve forests that protect water supplies. The final maps and data display development pressure on private forests in watersheds important for drinking water.