The city of Hilden drains the urban area predominantly in the separation system. In this system, the wastewater is collected and discharged separately from the rainwater. The wastewater is treated in the wastewater treatment plants on Düsseldorfer Straße and in Solingen Ohligs. In total, almost 99.8% of Hilden's inhabitants are connected to the public wastewater network. The wastewater treatment plants are operated by the Bergisch-Rheinischer Wasserverband.