Water treatment facilities strive to produce drinking water which is not only microbiologically safe (free from pathogens), but also ‘biologically stable’. The latter refers to the ability to maintain microbial quality of the water as the water is supplied through the drinking water distribution system (DWDS) pipe network, wherein microbial growth can recur. Although the DWDS presents an oligotrophic environment, significant microbial growth has been observed within the DWDS - in the bulk water, sediments, as well as surface biofilms. Such microbial growth in the DWDS causes hygienic, aesthetic, as well as operational concerns. There is lack of information and knowledge about the biofilm behavior and impacts in DWDS, owing in part to the challenges associated with conducting scientific studies on DWDS biofilms. Results from a long-term (30-month) bench-scale biofilm growth study are presented here. The study employed a representative approach having oligotrophic environment (reactors fed only with city tap water) to characterize temporal variation in biomass (using quantitative PCR of 16S rRNA genes), community composition (using Illumina MiSeq analysis), and physical morphology (thickness, density, porosity) of biofilms via confocal scanning laser microscopy (CLSM). The bench-scale biofilm community composition results are also compared with community analysis of actual water mains.