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Aims Bacterial community structure and composition of a drinking water network were assessed to better understand this ecosystem in relation to haloacetic acid ( HAA) degradation and to identify new bacterial species having HAA degradation capacities. Methods and Results Biofilm samples were collected from a model system, simulating the end of the drinking water distribution network and supplied with different concentrations of dichloroacetic and trichloroacetic acids at different periods over the course of a year. The samples were analysed by culturing, denaturing gradient gel electrophoresis ( DGGE) and sequencing. Pipe diameter and HAA ratios did not impact the bacterial community profiles, but the season had a clear influence. Based on DGGE profiles, it appeared that a particular biomass has developed during the summer compared with the other seasons. Among the bacteria isolated in this study, those from genus C upriavidus were able to degrade dichloroacetic acid. Moreover, these bacteria degrade dichloroacetic acid at 18°C but not at 10°C. Conclusions The microbial diversity evolved throughout the experiment, but the bacterial community was distinct during the summer. Results obtained on the capacity of C upriavidus to degrade DCAA only at 18°C but not at 10°C indicate that water temperature is a major element affecting DCAA degradation and confirming observations made regarding season influence on HAA degradation in the drinking water distribution network. Significance and Impact of the Study This is the first demonstration of the HAA biodegradation capacity of the genus C upriavidus. [ABSTRACT FROM AUTHOR]