The USEPA has regulated both chlorinated and brominated trihalomethanes (THMs) and haloacetic acids (HAAs) since Stage 2 D/DBP Rule. Among regulated species, all four chlorinated and brominated THMs are regulated as total TTHMs (TTHM). But of the nine HAAs, only the sum of five (HAA5) are regulated, with no detail on individual species. This leaves four unregulated HAAs of which all contain bromine. With more attention on the brominated haloacetic acids due to their higher toxicity, the focus on the formation of those unregulated brominated species is elevated. The objective of this study is to assess national occurrence of all brominated HAAs, together with the study of bromine incorporation which is used as an evaluation of relatively degree of bromination. In this research, both temperature and raw water bromine concentration are taken into consideration. Due to the fact that monitoring of bromodichloroacetic acid (BDCAA) is not widely done, bromochloroacetic acid (BCAA) was chosen to assess the HAA bromine incorporation. Statistical technologies were applied in the study to screen out unusable data. The result shows a strong relationship between seasons and disinfection byproduct (DBP) concentrations. Air temperature is also tested as a parameter of DBP formation. Selected HAA species biodegradation is also confirmed as an important role in DBP occurrence.