To ensure the security of urban drinking water, a study was conducted by taking the water source of Mopanshan Reservoir as the research sample, which has low temperature, low turbidity, high chroma, and is rich in natural organic matter. In the study, different disinfectant methods such as liquid chlorine, sodium hypochlorite, and chloramine disinfection were carried out in conventional water treatment process. The study indicated that the disinfection of liquid chlorine and sodium hypochlorite resulted in the formation of trichloroacetaldehyde. However, for the chloramine disinfection method, when the weight ratio of sodium hypochlorite and ammonium sulfate reached 4∶1 (2 mg/L∶0.46 mg/L), the by-product of disinfection especially trichloroacetaldehyde decreased significantly. Moreover, the disinfection lasted longer, which provided more stable disinfection effect for pipe-network water. Chloramine disinfection method was superior to conventional liquid chlorine and sodium hypochlorite disinfection in the decrease of by-products produced in drinking water disinfection, and its indexes met the requirements of Drinking Water Health Standards (GB5749-2006), which solved the problem of overmuch trichloroacetaldehyde in pipe-network water.