Chloramination and chlorination contribute to the formation of N-nitrosodimethylamine and trihalomethanes, respectively, both of which are defined as disinfection by-products. To be able to select the most appropriate water treatment scheme, it is important to comparatively evaluate the formation of both of these disinfection by-products during the application of different disinfection methods. In this study, chlorination, chloramination and stepwise chloramination methods have been applied to surface water samples that have been spiked with known N-nitrosodimethylamine precursors. Experimental results showed that ranitidine can be an effective N-nitrosodimethylamine precursor in distilled water, when chloraminated with high concentrations (140mg/L) for a long time (10days), resulting in approximately 450ng/L of N-nitrosodimethylamine. However, neither dimethylamine nor ranitidine leads to significant trihalomethanes or N-nitrosodimethylamine formation in lake water when chloramination is conducted with low concentration (2mg/L) for 2h. These results suggest that N-nitrosodimethylamine concentration measured in the effluent of the drinking water treatment plant may underestimate the N-nitrosodimethylamine concentration that will reach the consumers since chloramination reactions will continue in the distribution system. On the other hand, when only N-nitrosodimethylamine formation potential is used, it will overestimate the N-nitrosodimethylamine that might form in the distribution system due to high disinfectant concentration, high contact time and adjusted pH values used in the N-nitrosodimethylamine formation potential test.