Organic and inorganic nitrogen compounds are common in natural water, and compounds such as humic substances, amino acids, amines, ammonia, nitrites, and nitrates. Humic substances are generally large molecular weight compounds existing in soil. Amino acids and amines are the decomposition products of the living bodies, and their concentration in natural water ranges from parts per billion to parts per million levels (C. Le Cloirec, 1983). This study followed the organic nitrogen species from natural water through each stage of the drinking water treatment process, in order to observe their contributions to the DBP formation in different treatment processes. Based on these observations, the study also evaluated methods (pH adjustment, and use of coagulants and cationic polymers) of minimizing their effect on DBP formation. Humic substances are the most common precursor for trihalomethanes (THM) and THAA formation, but a preliminary study showed that the free chlorination of amino acids also contributed to the formation of DBPs. Approximately 2% or less of the carbon in original amino acid compounds transformed to THMs and THAAs. During chlorination of amino acids, aldehydes usually form as an intermediate stage. The aldehydes will further react with chlorine to form nitriles, acids, or other DBPs. This study found that even the polymer used as a coagulant aid can be a precursor of DBP formation. Phenylalanine, alanine, acetaldehyde and glyoxal were the compounds selected for chlorination and chloramination in 2 hours in a DI water. The behavior of alanine and phenylalanine in the same oxidation condition seems not much different in the DBP formation process. Chloroform transformation to the brominated THMs or nitriles from these two amino acids was slower than for aldehydes. The mechanism of nitrile formation from chloramination was unclear in this study. DBP analysis was performed on both bench test scale and full operation scale in different treatment stages. The results show that THM formation reached its endpoint within 2 minutes, but that THAAs need more than 6 hours. Further study is needed to understand the mechanism of the reaction. A series of tests was conducted for minimizing DBP formation. It was determined that the initial pH of the source water was a very important parameter for controlling the DBP formation. A lower pH condition at the right moment of coagulation significantly decreased the DBP formation, up to about 50 percent. Acid alum was then tested as a coagulant in order to reduce the DBP concentration. The result was positive. Tests showed that the DBP formation was reduced when polymer was not used in the treatment process. Additional tests showed that the order in which the polymer was added could effect the DBP formation. Adding the polymer prior to the alum had nearly the same effect as eliminating the polymer completely. Includes 6 references, tables, figures, appendix.