In the Jenfelder Au district of Hamburg, practical tests are being carried out to see how wastewater management can be sustainable in the city of the future. Instead of feeding used water from the bathroom, kitchen, and toilet into the local sewage system together – where it has to be elaborately cleaned using a great deal of energy – the different wastewater streams are separated right at the location and treated. The advantage: biogas can be obtained from the nutrient-rich sewage water from the 610 flats hooked up to the system and used to generate electricity and heat for the district. Purified wastewater from the shower or washing machine can be fed back into the local water cycle.