Biological safety of hot water is important, and it is affected by pipeline material to a certain degree. Polypropylene random (PPR), polyvinyl chloride (PVC) and stainless steel (SS) are the common materials for pipelines in domestic hot water systems (DHWS), and biofilm growth characteristics, and biofilm microbial communities and biological diversity on the walls of pipelines are affected by the pipeline materials to a certain extent. In this paper, the effects of different materials on the growth characteristics and diversity of microbial communities were studied. The results showed that after about 60 days, the bacteria of the biofilm on the wall of pipelines completed a microbial growth cycle. Compared with PPR and SS, a greater amount of the total number of bacteria, Escherichia coli and heterotrophic plate count (HPC) attached to the PVC pipeline. Although the types of bacteria on the pipelines were similar, the proportions of species were different. Proteobacteria were the dominant bacteria at the phylum level on all the walls of the PPR, PVC and SS pipelines, and the dominant bacteria at the genus level changed before and after the exfoliation of biofilm. Some potential pathogens, such as Pseudomonas and Legionella, were detected in biofilm, so effective biofilm disinfection should be considered to ensure biological safety in DHWS.