This paper describes the singular and composite effects of two catalysts; ultraviolet (UV) light and ultrasound (US) on the ozone (O3) oxidation of a purified solution of a commercially available humic acid with the objective of minimizing trihalomethane formation potential (THMFP). The principal findings are that (1) the most effective reactor conditions for both thedestruction of nonvolatile total organic carbon (NVTOC) and THMFP utilized both US and UV in combination with ozon, and (2) bicarbonate alkalinity reduces the oxidation efficiency of the US–UV–O3system apparently asa consequence ofradical scavenging.