The concept of the sponge city has become one of the central planning variables in urban development in China. A new green and blue infrastructure has taken priority on the urban surface to provide a convincing response to urban flash floods caused by heavy rainfall events. Rainwater is not only to be stored, but also used as a new water resource for urban water needs. In this way, there are still issues to be solved, such as how the pollution of precipitation/urban run-off can be removed, Thus, how to deal with plollution of urban run-off with tyre abrasion, fine and often particularly polluted particles as well as pathogens before rainwater is ready to be used in urban contextes.

The Beijing city government moves to the Tongzhou district. This was the reason to pilot the concept of the sponge city there - and with KEYS now also with German contribution. The key elements of the three-year project are the demonstrations. The KEYS network with 17 partners from Germany and China is working on optimizing existing sewer systems with regard to material retention, integrating retention soil filter technologies, introducing new sponge city elements, implementing mobile concepts for recording measurement data in urban catchment areas and further developing wastewater treatment not only with regard to the emerging pollutants.