This book describes the water security challenges with focus on water scarcity and quality in our rapidly changing world. Achieving water security is essential to promoting economic and social development, as well as resource sustainability and ecosystem integrity. Questions of water security are central to recent global agreements such as the Sustainable Development Goals (SDGs), the Paris Agreement on Climate Change, and the Sendai Framework for Disaster Risk Reduction. The thematic areas discussed here support the SDGs, with special attention to Goal 6 ("Ensure availability and sustainable management of water and sanitation"). The book is a collection of studies from engineering, social and environmental disciplines and aims at giving a balanced overview of the current , complex discourse on water scarcity and quality. It offers a source of inspiration and information for researchers, policymakers, planners, and practitioners concerning the further development of concepts, approaches, and methodologies for promoting water secure societies.