One of the most critical issues facing the United States today is the proper management of our water resources. Water availability and quality are changing due to increasing population, urbanization, and land use and climate change, and shortages in water supply have been increasing in frequency in many parts of the country. The National Science Foundation (NSF) has entertained the Water and Environmental Research Systems (WATERS) Network as one possible initiative whereby NSF could provide the advances in the basic science needed to respond effectively to the challenge of managing water resources. The WATERS Network, a joint initiative of the Engineering, the Geosciences, and the Social, Behavioral and Economic Sciences directorates at NSF, is envisioned as an integrated national network of observatories and experimental facilities supporting research, outreach, and education on large-scale, water-related environmental problems. The proposed observatories would provide researchers with access to linked sensing networks, data repositories, and computational tools connected through high-performance computing and telecommunications networks. This book, the final of a series about the WATERS project, provides a more detailed review of the Science Plan and provides advice on collaborating with other federal agencies.