This book expands the body of scientific knowledge on research and solutions for alternative water systems. It addresses a wide variety of water management issues in buildings, ranging from the technical possibilities, hydraulic and financial efficiency, and public acceptance of decentralized water systems, to their impact on sewage systems. Climate changes, population growth, and progressive urbanization are the main causes of the growing interest in alternative sources of water around the world. Decentralized systems are seen not only as solutions that can effectively save water, but also as systems that can operate partially or completely independently of centralized suppliers. With these aspects in mind, the main focus of this book is on showcasing a new approach to water management at the building scale. The findings and insights presented here will support the development of future technical guidelines for using alternative water systems in urban areas – an aspect that is particularly important since, in many European countries, these systems are only very rarely used.