The Hamburg Public Sewage Company is dedicated to the further development of the exist-ing urban water infrastructures. The aim is to prevent excessive use of resources. New cir-cular economy concepts are developed in conurbations including eco-sanitation in Hamburg as well as abroad. Sustainable handling of resources in the field of wastewater treatment is for the Hamburg Public Sewage Company not only a question in rural but also essential in urban areas. Wastewater treatment technology in conurbations in industrialised countries is a well established technology with a long history. Finding future solutions shall not focus on finding replacing alternatives but must include further development of the existing system. New water infrastructure systems designed for cities have a common feature: streams of substances are kept separate close to their sources. With the management of streams of substances (material flow management), individual parts of wastewater streams are collected, treated according to specific requirements and then returned to a production process (material recycling). The aim is to create processes which are almost complete cycles (circular economy). In the case of new communal supply and disposal concepts, the resources water, energy and nutrients are made available again for a new production cycle. This recy-cling enables substitutes to be used instead of primary resources. Primary energy sources are replaced with renewable raw materials and this results in a general reduction of resource consumption.