N-Nitrosamines are potent mutagenic and carcinogenic emerging water disinfection by-products (DBPs). The most effective strategy to control the formation of these DBPs is minimizing their precursors from source water. Secondary and tertiary amines are dominating precursors of N-nitrosamines formation during drinking water disinfection process. Therefore, the screening and removal of these amines in source water are very essential for preventing the formation of N-nitrosamines. A rapid, simple, and sensitive ultrafast liquid chromatography-tandem mass spectrometry (UFLC-MS/MS) method has been developed in this study to determine seven amines, including dimethylamine, ethylmethylamine, diethylamine, dipropylamine, trimethylamine, 3-(dimethylaminomethyl)indole, and 4-dimethylaminoantipyrine, as major precursors of N-nitrosamines in drinking water system. No sample preparation process is needed except a simple filtration. Separation and detection can be achieved in 11 min per sample. The method detection limits of selected amines are ranging from 0.02 µg/L to 1 µg/L except EMA (5 µg/L), and good calibration linearity was achieved. The developed method was applied to determine the selected precursors in source water and drinking water samples collected from Midwest area of the United States. In most of water samples, the concentrations of selected precursors of N-nitrosamines were below their method detection limits. Dimethylamine was detected in some of water samples at the concentration up to 25.4 µg/L.