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Evaluating microbial water quality changes in response to residential activities in a model home
Citation:
Tang, M., L. Boczek, H. Ryu, C. Muhlen, D. Williams, D. Lytle, M. Urbanic, P. Woodruff, M. McNeely, M. Pinelli, E. Crockett, AND C. Formal. Evaluating microbial water quality changes in response to residential activities in a model home. 2022 AWWA Water Quality Technology Conference, Cincinnati, OH, November 13 - 17, 2022.
Impact/Purpose:
This work showed that the culturable L. pneumophila, L. pneumophila gene markers, and heterotrophic plate count in hot water immediately increased following a simulated resident vacation (i.e., 10 days of no water use) and gradually returned to baseline levels at most taps with continued normal water use. Partial water plumbing drawdown (i.e., water lines completely drained but heater not drained) did not affect most taps while completely draining water heater decreased culturable L. pneumophila in some hot taps. Opening shower for 3-4 mins lowered microbial growth significantly. The results are informative for occupants to take measures to minimize risks associated with exposure to opportunistic pathogens such as Legionella in hot water.
Description:
Residential buildings exhibit characteristics of large surface area to volume ratio, reduced disinfectant levels, intermittent stagnation, and diverse plumbing surfaces. These characteristics provide a conducive environment for microbial proliferation and growth within plumbing surface biofilms, including opportunistic pathogens that cause infectious disease. Appropriate preventive and mitigation measures to control the microbial growth is necessary to reduce the exposure of homeowners. However, limited data and guidance are available to inform homeowners of the potential impacts of their residential activities such as taking long vacation, partial home plumbing drawdown during plumbing or fixture repair, and completely draining water heater tank as recommended by manufacturer for maintenance purposes. The goal of this was to evaluate the microbial (e.g., heterotrophic plate count (HPC), culturable L. pneumophila, and L. pneumophila gene markers) water quality changes within a model home following these practices. The model home (HPS) used in this study was initially constructed in Cincinnati, OH to study lead and copper corrosion, and later was found contaminated with Legionella. The HPS was connected to a Cincinnati building water outlet, and consisted of a shower, 40-gallon electric hot water tank, a toilet, a recirculation pump, a water meter, and four faucets that are connected via copper piping, lead service line, leaded brass fixtures, and leaded solder joints. During the 8-month study, the HPS simulated occupation and water use patterns of four people and underwent a flush protocol of ~75 gallons/day by flushing the faucets, toilet, and shower head. Cold and hot microbial sampling, and metal sampling were conducted from faucets, shower head, and water heater tank after overnight or weekend stagnation before and after each simulated activity. Our results showed that the simulated residential activities did not significantly change microbial growth in cold water samples. However, in hot water samples, the culturable L. pneumophila, L. pneumophila gene markers, and HPC immediately increased following a simulated resident vacation (i.e., 10 days of no water use) and returned to baseline levels at most taps within 2 weeks with continued normal water use. Partial water plumbing drawdown (i.e., water lines completely drained but heater not drained) did not affect most taps while completely draining water heater decreased culturable L. pneumophila in some taps. Opening shower for 3-4 mins (i.e., flushing out 12-15 liters of water) reduced microbial growth significantly compared to the start of shower. Additionally, the impact of stagnation time, draw of samples (1st vs 2nd), sampling location (cold vs hot), water use, and water quality (e.g., pH, chlorine, temp) on microbial growth and metals were also evaluated, along with their associations. The results are useful for occupants to take measures when their home is contaminated with Legionella.