Ground water is among the Nation's most important natural resources. It provides drinking water to urban and rural communities, supports irrigation and industry, sustains the flow of streams and rivers, and maintains riparian and wetland ecosystems. In many areas of the Nation, the future sustainability of ground-water resources is at risk from over use and contamination. Because ground-water systems typically respond slowly to human actions, a long-term perspective is needed to manage this valuable resource. The U.S. Geological Survey Ground-Water Resources Program provides fundamental data, regional evaluation, and predictive tools to help assure the sustainability of our Nation's ground-water resources.