A two-block full-factorial matrix was designed to statistically evaluate the influence of bromide ion on the formation and speciation of haloacetic acids (HAAs) during chlorination and the effects of independent variables, including pH, reaction time, and chlorine dosage. Almost all of the independent variables were positively correlated with the formation of HAAs. Bromide ion was shown to shift the distribution of HAAs (as well as trihalomethanes) to more brominated species. Not only were purely brominated acetic acids formed, but also mixed bromine and chlorine species-which were measured for the first time.