Takustraße 7 D-14195 Berlin-Dahlem Germany Konrad-Zuse-Zentrum f¨ ur Informationstechnik Berlin J ENS BURGSCHWEIGER,B ERND GN ¨ ADIG, AND MARC C. S TEINBACH Nonlinear Programming Techniques for Operative Planning in Large Drinking Water Networks ZIB-Report 05-31 (July 2005)