The water cycle is strictly related to the fair and sustainable development of any society. Appropriate technologies and practices are needed for providing clean water and adequate sanitation to citizens worldwide, while facing environmental and societal challenges, such as climate change and increasing urbanization. Wastewater treatment facilities are nowadays shifting from infrastructures providing effective clean water, sanitation and environmental protection towards advanced biorefineries that can recover valuable resources (as reusable water, biopolymers and nutrients) from wastewater, while aiming at more stringent effluent quality targets, at energy neutrality, and at lowering the overall environmental impact. This MOOC is aimed at providing key elements in relation to the management of the urban water cycle, including both conventional goals and the challenges of the smart cities of the future. This MOOC presents a full picture, although very concise, of present and emerging technologies for wastewater treatment, presented by professors teaching at Politecnico di Milano.