1. Diplom-Ingenieur, Institut fuer Systemdynamik (ISYS), Universitaet Stuttgart, Pfaffenwaldring 9, 70569 Stuttgart, Germany (corresponding author).
2. Senior Lecturer, Centre for Water Systems, Univ. of Exeter, Harrison Bldg., North Park Rd., Exeter EX4 4QF, U.K.
3. KWR, P.O. Box 1072, 3430 BB Nieuwegein, The Netherlands.
4. Professor, Centre for Water Systems, Univ. of Exeter, Harrison Bldg., North Park Rd., Exeter EX4 4QF, U.K.