The rainwater is fed from the roof and the road into the rainwater canal. From there it is discharged into the river. If too much rainwater flows off, part of it is stored in rainwater retention basins. The rainwater channel is much larger than the sewage channel.

The domestic wastewater is led into the wastewater channel and then to the wastewater treatment plant. The sewer is located below the rainwater sewer so that the rainwater can be contaminated in the event of leakages in the sewers.

• Higher purification efficiency of the wastewater treatment plant due to more uniform inflow
• No dirty water is discharged into the river untreated

• Higher investment and maintenance costs than a mixed system (two channels)
• Maintenance-intensive (two channels)
• Dirty rainwater (e.g. from the road) is discharged untreated into the river