The use of chlorine dioxide as a disinfectant in the treatment of drinking water constitutes a good alternative to limit the formation of chlorinated by-products, However, chlorine dioxide reactions produce chlorites and chlorates which may be a health risk. This paper studies the impact of several drinking-water treatments on chlorine dioxide demand and on chlorite and chlorate formation, The treatments investigated were: direct sand filtration, ozonation, and second stage biological activated carbon (BAG) filtration. The results showed a decrease in chlorine dioxide demand and chlorite formation following these treatments, However. only ozonation and second stage biological activated carbon (BAG) filtration were able to lower chlorate formation. Interestingly, the decrease in chlorine dioxide demand by BAC filtration was more pronounced when a lower chlorine dioxide dosage was applied, while the chlorine dioxide dosage did not seem to influence chlorite formation. This study shows the analytical difficulties associated with chlorine dioxide demand measurements as opposed to chlorite and chlorate measurements by ionic chromatography. However, it also shows that chlorite and chlorate measurements could not replace chlorine dioxide demand measurements. Finally, this study proves the applicability of a second order model to describe short-term chlorine dioxide demand.