Ground water is the Nation's principal reserve of fresh water and represents much of its potential future water supply. Ground water on National Forest System (NFS) lands is a major contributor to flow in many streams and rivers and has a strong influence on the health and diversity of plant and animal species in forests, grasslands, riparian areas, lakes, wetlands, and cave systems. It also provides drinking water to hundreds of communities. Demands for safe drinking water and requirements to maintain healthy ecosystems are increasing, and complex social and scientific questions have arisen about how to assess and manage the water resources on NFS lands. This technical guide was developed to help address these issues. It describes the national ground water policy and provides management guidelines for the NFS.