This book presents possible solutions for a circuler economy (CE)  in the water and wastewater sector through an inventory of multidisciplinary knowledge with high scientific and practical importance which can contribute to support the transition to the CE model in water and wastewater sector. Water in modern studies exceeds being an important source for irrigation and drinking. It is now a significant source of renewable energy and a catalyst in most industrial and manufacturing products. The protection and sustainable management of water resources and water-based waste (as wastewater, sewage sludge, or sewage sludge ash) are important aspects of the CE, which is defined as a regenerative growth model that gives back to the planet more than it takes. Our book, entitled "Water in Circular Economy", delivers a comprehensive overview of the latest research covering the following aspects of water management from the perspective of the CE implementation: ·       Water as a key resource in the circular economy;·       Innovative solutions in transition to the circular economy in water and wastewater sector;·       Monitoring of circular economy implementation in water and wastewater sector.