1. Institute for Water Quality and Waste Management, Vienna University of Technology, Karlsplatz 13, 1040 Vienna, Austria (E-mail: otto.nowak@tuwien.ac.at; mzessner@iwag.tuwien.ac.at)
2. Institute for Urban Water Management, Dresden University of Technology, Mommsenstrasse 13, 01062 Dresden, Germany (E-mail: kuehn@rcs.urz.tu-dresden.de)