Life, in combination with solar radiation and abiotic processes, is most probably the reason why liquid water has existed on Earth for over billions of years, and the global mean temperature has remained in a life-enabling range. Efforts to limit or even reverse global warming must be derived from the knowledge of the Earth’s complex life-support system. In this context, the balance between liquid and gaseous water plays a crucial role, and water management becomes an important field of innovation and action, globally, on the scale of watersheds but also on the very local level. Cascading use, reuse, and temporary storage of water in urban settings must be considered to limit over-extraction of water from natural resources, and to maintain the life supporting function of ecosystems. At the same time, public health requirements, cost efficiency, and reliability demands are to be met.