Haloacetic acids (HAAs) are disinfection by-products often found in chlorinated drinking water. Because HAAs are suspected carcinogens, the EPA maximum for the five regulated haloacetic acids (HAA5) in municipal water is 60 μg/L. In a drinking water distribution system, HAAs may be degraded by bacteria present in the biofilm along the pipes. In this work, products and relative rates of HAA biodegradation were studied using crude haloacid dehalogenase harvested from Xanthobacter autotrophicus. HAAs tested were mono-, di-, and trichloroacetic acids; mono- and dibromoacetic acids; bromochloroacetic acid; and mixtures of two of the above HAAs in competition studies. Complete analysis of each HAA/enzyme assay was possible with ion chromatography, since the organic products (glycolate, glyoxylate, and oxalate) retain the original HAA carboxylate group. Analyses of monochloroacetate (MCA) and dichloroacetate (DCA) competition assays showed that MCA degraded more rapidly than DCA when the two HAAs were competing for the same enzyme; interestingly, in their individual assays, the rate of degradation of MCA was slower than that of DCA. A possible explanation is that MCA is better able to bind to the enzyme active site than DCA, but subsequent SN2 displacement of chloride that occurs within the active site is faster for DCA.