The formation potential of four trihalomethanes (THMFP) and seven haloacetic acids (HAA7FP) in 13 source waters taken from four major water basin areas in China was evaluated using the simulated distribution system (SDS) chlorination method. The specific ultraviolet absorbance (SUVA254: the ratio of UV254 to dissolved organic carbon (DOC)), which ranged between 0.9 and 5.0 L/(mg x m), showed that the organic compounds in different source waters exhibited different reactivities with chlorine. The HAA7FP of source waters ranged from 20 to 448 microg/L and the THMFP ranged from 29 to 259 microg/L. The HAA7FP concentrations were higher than the THMFP concentrations in all but one of the samples. Therefore, the risks of haloacetic acids (HAAs) should be of concern in some source waters. TCM (chloroform) and BDCM (bromodichloromethane) were the major THM constituents, while TCAA (trichloroacetic acid) and DCAA (dichloroacetic acid) were the major HAA species. Br-THM (brominated THM species) were much higher than Br-HAA (brominated HAA species), and the formation of Br-DBP (Br-THM and Br-HAA) should be of concern when the bromide concentration is over 100 microg/L.