Unplanned transportation systems near water resources have not only caused a dramatic population increase in the water catchment areas of Istanbul but also created major water pollution problems as a result of illegal settlement and industrial and agricultural activities. In this study, water qualities in seven main water reservoirs of Istanbul were monitored for I year. The water was found to be highly polluted in all reservoirs. Also bromide levels of these reservoirs were monitored for the first time for the evaluation of applicability of ozone oxidation for the treatment of raw waters. Bromide level was found very high in the Buyuk Cekmece (BC) reservoir. Thus, ozone was applied to determine bromate formation potential of BC raw water and to optimize ozone and coagulation processes for bromate control in bromide-containing BC surface water. An optimum ozone/TOC ratio and aluminum sulfate dose were determined as 0.8 mg/mg and 40 mg/l for the control of bromate formation. TOC (50%) was removed after coagulation of previously ozonated BC water.