Microbial Dynamics of Drinking Water Quality Within Building Plumbing

Building plumbing systems play a critical but often overlooked role in shaping the chemical and microbiological quality of drinking water delivered to occupants. Common events such as vacations, property sales, and seasonal closures, can result in extended stagnation of building plumbing. Under stagnation, physicochemical changes can occur allowing for potential issues such as heavy metals from plumbing materials (e.g., lead, copper) and growth of drinking water-associated pathogens that can cause infections in immunocompromised individuals (DWPI) (e.g., Legionella pneumophila, Pseudomonas aeruginosa, nontuberculous mycobacteria). While water quality deterioration during stagnation has long been recognized, the widespread building shutdowns during the COVID-19 pandemic revealed fundamental gaps in understanding how building water changes under extended stagnation and whether common remediation practices are effective. These gaps were addressed through a set of controlled experiments on four identically-built, large-scale plumbing systems (each equipped with a water heater tank and triplicate 50 foot copper pipe runs) to assess A) stagnation and B) flushing, and C) a systematic review of extended stagnation studies conducted within actual buildings.