Treatise on Water Science is an essential reference for researchers and policy makers addressing some of the most pressing problems of our time. Despite the notable progress achieved in recent decades in our understanding of technologies and management strategies pertaining to water resources, far too many of the world's residents still lack access to a safe, reliable, and affordable water supply. Many residents also are impacted severely by droughts and floods in ways that impair their ability to achieve and sustain food security, while threatening their livelihoods. And the frequency of droughts and floods is likely increasing in some regions due to climate change. Researchers will continue seeking solutions to problems involving water allocation and supply, demand management, water quality, sanitation, and the use of wastewater for irrigation. Solutions will require a keen understanding of water science, management, and policy. Information presented in the Treatise will inspire and support scientists engaged in both the basic and applied research needed to determine the best possible water management policies and investment opportunities. While focusing primarily on the scientific aspects of water resources, this new edition of Treatise on Water Science aims to be of value to those who study, design, and implement water policies and management programs. By providing ready access to scientific principles and research findings regarding water resources for those who formulate management strategies and policies, the Treatise will give tangible contributions to expand water access, improve livelihoods, and enhance food security around the world.