||Brominated disinfection byproducts (Br-DBPs) are generally more cytotoxic and genotoxic than their chlorinated analogues. A great portion of total organic bromine in disinfection of drinking water is still unknown and may be ascribed to polar Br-DBPs. In this work, a novel approach, precursor ion scan (PIS) using ultra performance liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry (UPLC/ESI-tqMS), was adopted and further developed for selective detection and identification of new polar Br-DBPs in chlorination, chloramination, ozonation and chlorine dioxide treatment. In the ESI-tqMS PIS spectra, adducts of polar compounds could overlap with higher molecular weight (MW) DBPs, which may complicate ESI-tqMS spectra. A new method was developed for differentiating adducts of common DBPs from higher MW DBPs, using ESI-tqMS PISs of the molecular ions of common DBPs. Ions with the same m/z values could overlap in ESI-tqMS PISs too, so UPLC was coupled to ESI-tqMS to separately detect new polar Br-DBPs. The separation characteristics of UPLC were examined with 21 bromine-containing standard compounds. In chlorination, 34 new polar aromatic and unsaturated aliphatic Br-DBPs were detected and tentatively proposed with chemical structures, of which 2,4,6-tribromophenol, 3,5-dibromo-4-hydroxybenzoic acid, 2,6-dibromo-1,4-hydroquinone and 3,3-dibromopropenoic acid were confirmed with authentic standards. High MW Br-DBPs underwent decomposition to relatively low MW Br-DBPs or finally to haloacetic acids and trihalomethanes. The “black box” from the input of “humic substances + bromide + chlorine” to the output of “haloacetic acids + trihalomethanes” was opened to a significant extent. The effect of the Cl2/C ratio on the formation of polar Br-DBPs varied with DBP species. Generally, high Cl2/C ratios generated high levels of polar Br-DBPs, but reduced the formation of some intermediate polar Br-DBPs. Low pH favored the formation of most polar Br-DBPs, but accelerated the decomposition of some intermediate polar Br-DBPs in short chlorine contact times. Three different types of natural organic matter generated many identical Br-DBP species but at different levels. In chloramination, 26 aliphatic, aromatic, or nitrogenous polar Br-DBPs were newly detected, of which 2,4,6-tribromo-resorcinol, 2,6-dibromo-4-nitrophenol, and 2,4,4-tribromo/dibromochloro/bromodichloro-1-hydroxy-cyclopentene-3,5-diones were identified or partially identified. These polar Br-DBPs were slowly accumulated in water. The formation of Br-DBPs inhibited the formation of chlorinated DBPs. Low pH significantly favored the formation of polar Br-DBPs. Low levels of polar Br-DBPs were generated in ozonation alone. The effect of preozonation on the formation of polar Br-DBPs depended on ozone dose, DBP species and subsequent disinfection process. Generally, the high ozone dose reduced the formation of most polar Br-DBPs, whereas the low ozone dose enhanced that; the enhancement on the formation of new polar Br-DBPs as a result of preozonation was more significant in chloramination and chlorination-chloramination than in chlorination. A significant amount of polar Br-DBPs were generated in the prolonged chlorine dioxide treatment. Chlorine dioxide pretreatment increased polar Br-DBP precursors and thus increased the formation of polar Br-DBPs in the subsequent chloramination. However, chlorine dioxide pretreatment reduced the formation of polar Br-DBPs in the subsequent chlorination.