Haloacetaldehydes (HAs) represented the third major class of halogenated disinfection byproducts (DBPs) formed (on a weight basis) in many of the waters in this study. Although the plants in this study used a wide variety of disinfectants and chlor(am)inated the water at a wide range of pH levels, the percentage of HAs that were dihalogenated tended to correlate with the percentage of haloacetic acids (HAAs) that were dihalogenated. Typically, the haloacetonitriles (HANs) were produced at approximately one-tenth the level of the trihalomethanes (THMs) (on a weight basis). Alternatively, there appeared to be a better relationship between dichloroacetonitrile (DCAN) and dichloroacetic acid (DCAA) formation for samples chlorinated at an acidic pH level. The relative speciation of brominated and chlorinated dihalonitromethanes was comparable to that of the dihalogenated HAAs and HANs. Likewise, the relative speciation of the trihalonitromethanes was similar to that of the trihalogenated HAAs and the THMs. Chloramination formed certain dihalogen-substituted DBPs (HAAs, HAs) preferentially over related trihalogenated species. In addition, chlorine dioxide produced dihalogenated HAAs. Carboxylic acids represented a significant portion of the assimilable organic carbon (AOC) produced during ozonation. Moreover, the formation and removal of carboxylic acids and AOC tended to follow the same trends through the different treatment processes. Includes 17 references, tables, figures.