This paper presents the results from preliminary design of the ozonation system for the largest water treatment plant in the Netherlands. The Berenplaat Water Treatment Works (WTW) in Rotterdam is one of five facilities supplying water to South Holland by the South Holland South Water Works. (SHSWW). Witteveen+Bos and Montgomery Watson were engineering partners in the preliminary design of the entire facility modifications that included GAC for AOC removal and water stabilization following ozonation and UV for final disinfection. The 18,000 m3/hr water treatment plant will produce biologically stable finished water without the use of chlorine within the treatment plant or as a final disinfectant. Background data on the Berenplaat WTW and this project are provided in the first section of the paper. The methodology used to develop ozonation requirements for both disinfection and oxidation are presented in the second section. The results of the study are included in the final section with the preliminary design criteria that were developed.