There are some differences between the municipalities. Rainwater that cannot infiltrate into the soil due to sealed (or partially sealed) surfaces must:
a.) be infiltrated on the property via infiltration systems (trenches, basins, or shafts)
b.) be discharged into the municipal rainwater drainage network (if available)
or
c.) be discharged into the regular sewer network
With us, it is also the case that rainwater from all (partially) sealed surfaces (roof, terrace, yard/driveway/parking space) should preferably infiltrate on the property. Discharge would also have been possible here, but probably would not have saved money and would also mean additional drainage fees.
We had the infiltration system calculated through our construction supervisor and the result was 13 boxes from Intewa with the dimensions 80*80*36 with a total volume of 2.78 m³.
According to our soil report, we have a kf-value of 5*10^-5. The water level on the day of the investigation was 1.9 m - 1.7 m. However, the report also stated a design water level of 0.4 m below the reference point. That is probably our worst-case scenario, right?