Stagnant plumbing: Drinking water quality responses to stagnation in controlled systems.

Despite the high frequency of extended building closures from vacations, property sales, or building closures, relatively little is known about how water quality reacts during extended plumbing stagnation. Short periods of stagnation are known to result in chemical and microbial water quality degradation. Several 2020 studies in real buildings investigated extended stagnation, but real-world studies often lack control, and it thus remained unclear what periods of stagnation may be problematic. This study examines the impact of varying stagnation regimes (flushed daily, weekly, biweekly, and monthly) on the chemical and microbial water quality dynamics in controlled, large-scale plumbing systems. In this study, extended stagnation regimes (alternating biweekly and monthly) had similar results, and increased stagnation was associated with evidence consistent with scale formation and particulate settling in tanks. Weekly stagnation, a condition chosen to represent common flushing protocols, often showed similar results to extended stagnation regimes. The flushing regime was insufficient to prevent the growth of bacteria such as potential sulfate-reducing bacteria and potential drinking water pathogens, specifically Mycobacterium spp. While daily use controlled microbial growth, the pipes had elevated copper levels, potentially attributed to a lack of scale formation in the newly constructed plumbing system. These results underscore the need for revised water management strategies to ensure safe drinking water in low occupancy buildings. Current recommendations may have inadequate flushing protocols, and any benefits need to be weighed against their costs (e.g., labor, time).