Superoxide radicals (O₂^•-) have been suggested as an important chain carrier in the radical chain reaction that promotes ozone (O₃) decomposition to hydroxyl radicals (^•OH) during ozonation. However, due to the difficulty in measuring transient O₂^•- concentrations, this hypothesis has not been verified under realistic ozonation conditions during water treatment. In this study, a probe compound was used in combination with kinetic modeling to evaluate the role of O₂^•- for O₃ decomposition during ozonation of synthetic solutions with model promotors and inhibitors (methanol and acetate or tert-butanol) and natural waters (one groundwater and two surface waters). By measurement of the abatement of spiked tetrachloromethane (as a O₂^•- probe), the O₂^•- exposure during ozonation was determined. Based on the measured O₂^•- exposures, the relative contribution of O₂^•- to O₃ decomposition, in comparison to OH^-, ^•OH, and dissolved organic matter (DOM), was quantitatively evaluated using kinetic modeling. The results show that water compositions (e.g., the concentration of promotors and inhibitors, and the O₃ reactivity of DOM) have a considerable effect on the extent of the O₂^•--promoted radical chain reaction during ozonation. In general, the reaction with O₂^•- accounted for ∼59-70% and ∼45-52% of the overall O₃ decomposition during ozonation of the selected synthetic solutions and natural waters, respectively. This confirms that O₂^•- plays a critical role in promoting O₃ decomposition to ^•OH. Overall, this study provides new insights on the controlling factors for ozone stability during ozonation processes.