Measurements of the Total Organic Halogens (TOX) produced in the National WaterCarrier(NWC) of Israel after disinfection with chlorine dioxide revealed that compared to chlorine, ClO2forms only a very small amount of chlororganic compounds. Mixtures of Cl2and ClO2that have been reported to reduce the concentrations of both the chlorinated organics as well as the chlorite Ions produced by ClO2, were found not to be very useful because of the fact that high bromide concentrations are present In the NWC. Therefore high ratios of ClO2/Cl2are needed to reach a significant reduction in Trihalomethanes (THM's). The amount of THM's can however be satisfactorily reduced when ClO2is introduced a few hours before chlorine.