Impacts of household water demands and water heater delivery temperatures on opportunistic premise plumbing pathogens (OPPPs) in a residential setting

• OPPP absence in water supply did not negate subsequent growth in plumbing system. • Faucets pose higher risk of exposure to L. pneumophila compared to tubs and showers. • Fewer detections of L. pneumophila with distance from potential growth site to tap. • QMRA models with this dataset can estimate potential risk of infection with OPPPs. Efforts aimed towards water and energy conservation within residential buildings may create enhanced conditions for Opportunistic Premise Plumbing Pathogens (OPPPs) growth. To investigate this issue, a study was conducted to assess the effect of water demands and water temperature on four OPPPs – L. pneumophila, P. aeruginosa, M. avium, and N. fowleri – in a residential test facility. Two water delivery temperatures (54 and 66 °C) and household water demands (low: 47.3 or 127.9 L; high: 263.1 L) were evaluated. A total of 260 samples were collected and analyzed using droplet digital polymerase chain reaction (ddPCR). Samples were collected from the influent water pipe, water heater, PEX manifold, kitchen and bathroom faucets, tub, and shower. The most frequently detected OPPP was L. pneumophila , which was found in 8.1 % of water samples, followed by P. aeruginosa (3.5 %), and M. avium (1.9 %). Water demand and water heater setpoint temperature were independently associated with the detection and concentration of L. pneumophila . Kitchen and bathroom faucets posed a higher risk of exposure to L. pneumophila compared to the tub and shower. The current dataset represents the largest-scale investigation to date of the effect of household operating conditions on OPPPs. This dataset can be used in quantitative microbial risk assessment (QMRA) models to estimate the potential risk of infection with OPPPs. Minimal research exists on opportunistic pathogens in residential settings. This study may help the plumbing industry improve practices for building water systems to control the growth of OPPPs.