Effect of Water Chemistry, Pipe Material, Temperature and Flow on the Building Plumbing Microbiome and Opportunistic Pathogen Occurrence

The building plumbing microbiome has important implications, especially in terms of its role as a reservoir and conduit for the spread of opportunistic pathogens (OPs), such as Legionella pneumophila. This dissertation applied next-generation DNA sequencing tools to survey the composition of building plumbing microbiomes and assessed hypothetical factors shaping them.

A challenge to identifying key factors shaping building plumbing microbiomes is untangling the relative contributions of influent water quality, provided by drinking water utilities, and those of building-level features, such as pipe materials. To this end, standardized pipe rigs were deployed at the treatment plants and in distal portions of the water distribution system at five water utilities across the eastern U.S. Source water and treatment practices appeared to be the overarching factors shaping the microbial taxonomic composition at the tap, with five key water chemistry parameters identified (total chlorine, pH, P, SO42- and Mg2+).

Hot water plumbing is of particular interest because OPs tend to proliferate in warm water environments and can be inhaled in aerosols when showering. Two identical lab-scale recirculating hot water rigs were operated in parallel to examine the combined effects of water heater temperature set point, pipe orientation, and water use frequency on the hot water plumbing microbiome. Our results revealed distinct microbial taxonomic compositions between the biofilm and water phases. Importantly, above a threshold of 51 °C, water heater temperature, pipe orientation, and water use frequency together incurred a prominent shift in microbiome composition and L. pneumophila occurrence.

While heat shock is a popular means of remediating L. pneumophila contamination in plumbing, its broader effects on the microbiome are unknown. Here, heat shock was applied to acclimated lab-scale hot water rigs. Comparison of pre- versus post- heat shock samples indicated little to no change in either the microbial composition or L. pneumophila levels at the tap, where both water heater temperature and water use frequency had the most dominant effect.

Overall, this dissertation contributes to advancing guidance regarding where to most effectively target controls for OPs and also advances research towards identifying the features of a 'healthy' built environment microbiome.