Building plumbing microbial communities can significantly influence water quality at the point of use, particularly during periods of stagnation. Thus, a fine-scale understanding of factors governing community membership and structure, as well as environmental and ecological factors shaping building plumbing microbial communities is critical. In this study, we utilized full-length 16S ribosomal RNA (rRNA) gene sequencing to investigate the microdiversity and spatial-temporal dynamics of microbial communities in institutional and residential building plumbing systems. Bacterial operational taxonomic units (OTUs) within institutional buildings exhibited much lower microdiversity relative to the same OTUs in residential buildings. Higher microdiversity was associated with higher persistence and relative abundance of OTUs. Interestingly, amplicon sequencing variants within the same OTUs exhibited habitat preferences based on the building type while also demonstrating varying temporal turnover patterns. Dispersal limitation disproportionately governed community assembly in institutional buildings, whereas heterogeneous selection was the dominant ecological mechanism shaping the microbial community in residential buildings. Dispersal limitation in institutional buildings is consistent with larger building sizes and greater periods of water stagnation. Interestingly, the inability to explain the extent of heterogeneous selection-driven community assembly in residential locations using measured water chemistry may suggest a disproportionately large effect of fine-scale variation in plumbing characteristics on community assembly in residential locations.