The Reinhalteverband Mühltal & Region Böhmerwald in Upper Austria consists of 24 municipalities, looks after around 1.000 km of sewer, 18.000 sewer shafts, 300 pumping stations, 60 storm waterbasins and 6 sewage treatment plants. Despite its size, however, the drainage system reached its limits. The individually operated storm waterbasins, for example, relieved the load rigidly into the recipient in the event of overload. The fixed outflow rate to the sewage treatment plant also proved not to be optimal, as the catchment areais often irrigated unevenly. In order to reduce the untreated discharge quantities, additional storage basins could have been built or the existing basin volumes could have been increased. However,these measures are associated with considerable costs, which is why the Reinhalteverband decided to coordinate the control of the basins.