The impacts of alum coagulation on the distribution of disinfection byproducts (DBPs), trihalomethanes (THMs) and haloacetic acids (HAAs), were evaluated under controlled chlorination conditions using four surface waters. Among the nine HAAs found in waters, dihaloacetic acids (X₂AAs) have been found to be the dominant species in all of the raw and alum treated waters. Alum coagulation tends to remove more monohaloacetic acids (XAAs) and trihaloacetic acids (X₃AAs) precursors than that of dihaloacetic acids (X₂AAs). Alum coagulation treated water had a lower HAA₉/TTHM ratio compared with that of the raw water. The increase of THM bromine incorporation factors (BIF_α) value of alum treated water was statistically significant in comparison with the raw water. On average, BIF_α increased by 54% after the alum coagulation process in these four different waters. This indicated that THM speciations shifted in favor of the more brominated compounds. However, alum coagulation treatment process had less effect on HAA bromine incorporation factors (BIF_ß) than it did on BIF_α. Bromine Incorporation Factor (BIF) values decreased with time in the THM and HAA formation processes, especially within the first 10 hours of the reaction time. This suggested that brominated THMs or HAAs formed faster than the chlorinated species in the initial period. Includes 22 references, tables, figures.