Bacterial community structure and iron corrosion were investigated for simulated drinking water distribution systems (DWDSs) composed of annular reactors incorporating three different treatments: ozonation, UV/chlorine, and UV/monochloramine. The results showed that the bacterial community structure was significantly affected by the treatment type, with ozonation being the most effective in reducing the bacterial load. Iron corrosion was also significantly affected by the treatment type, with UV/chlorine being the most effective in reducing iron corrosion. The study provides valuable insights into the effects of different treatments on bacterial community structure and iron corrosion in DWDSs, which can inform the development of more effective treatment strategies.