Comprehensive control of regulated trihalomethanes (THMs) and haloacetic acids (HAAs), as well as nitrosamines, is needed to address forthcoming regulations. The formation potentials (FPs) of these disinfection by‐products (DBPs) with chlorination (Cl2) and chloramination (NH2Cl) were investigated along the treatment train of a conventional and ozone‐biologically active carbon (O3‐BAC) process. The nitrosamines FP‐NH2Cl, THM FP‐Cl2, and HAA FP‐Cl2 in heavily impacted source water in China were as high as 333 ng/L, 307 µg/L, and 247 µg/L, respectively, indicating that there was a high risk of DBP formation in the finished water. A combination of conventional and O3‐BAC processes reduced nitrosamine FP‐NH2Cl to 39 ng/L, achieving an 88% removal. This process also reduced THM FP‐Cl2 and HAA FP‐Cl2 to 197 and 174 µg/L, with fairly low removals of 36 and 29.5%, respectively. The strategy for this water was to apply conventional and O3‐BAC processes to substantially eliminate nitrosamine precursors and then apply chloramination to control THMs and HAAs.