Background In urban areas all over the world, the treatment of rainwater collected in a separate sewage system is a common problem, for which many different solutions are applied. If no surface waters are available as a runoff option, the rainwater is percolated and cleaned in filter systems. If surface waters are available as a runoff option, the rainwater is not cleaned or retained before being discharged. This is unsatisfactory from an ecological point of view. Throughout Europe, standards and regulations relating to the treatment of rainwater are evolving. In the new EU Member States in particular, the trend is to have a separate sewage system, which is likely to aggravate the problem of rainwater treatment and management. Objectives The “RAINMAN” project would demonstrate a new process technology combining several treatment stages for polluted urban rainwater, e.g. water running off from roads. This process is characterised by a mechanical cleaning stage, a deflocculating stage, flood meadows acting as a retention and balancing area and finally a percolation dam. For these process stages, a closed wastewater treatment plant (Kläranlage Blumental) would be adapted. It was expected, that this treatment will result in an environmentally compliant load of organic matter and suspended solids discharged into the river Liesing. Furthermore, the new plant would enable rainwater management and the prevention of floods. Due to the separate treatment, rain water would no longer be conducted to the centralised wastewater treatment plant (WWTP). The WWTP would therefore be relieved from hydraulic load and it would be possible to operate it more economically. Results The project did not achieve its objectives and expected results.