Acknowledging that resource efficiency as well as ecosystem protection are crucial goals to tackle has led to a deep rethinking in the way wastewater has been dealt with up to the 20th century. Indeed, pollution reduction to harmless levels has been the main focus of conventional wastewater treatment plants which have deployed effective and reliable solutions to get rid of suspended and dissolved pollutants. Nowadays, those same wastewaters are looked at as a mine of valuable resources that are to be harvested from the sewage through efficient technologies operated within water and resource recovery facilities (formerly known as wastewater treatment plants).Rethinking the way we deal with wastewater has become the new challenge and a key tool to implement the Circular Economy Action Plan, to address numerous UN Sustainable Development Goals, as well as to provide support tools to improve resilience to environmental and global threats, including climate change, water and food security, epidemic outbreaks and political instability.To tackle these challenging goals, new technologies as well as multidisciplinary tools are needed to pave the way toward a new water-economy, including: innovative technologies, integrated and risk-based approaches, and adequate regulatory and economic guidelines to promote technological uptake and societal acceptance.In Focus a book series that showcases the latest accomplishments in water research. Each book focuses on a specialist area with papers from top experts in the field. It aims to be a vehicle for in-depth understanding and inspire further conversations in the sector.