Reductions in nonresidential water demand during the COVID-19 pandemic highlighted the importance of understanding how water age impacts drinking water quality and microbiota in piped distribution systems. Using benchtop model distribution systems, we aimed to characterize the impacts of elevated water age on microbiota in bulk water and pipe wall biofilms. Five replicate constant-flow reactors were fed with municipal chloraminated tap water for 6 months prior to building closures and 7 months after. After building closures, chloramine levels entering the reactors dropped; in the reactor bulk water and biofilms the mean cell counts and ATP concentrations increased over an order of magnitude while the detection of opportunistic pathogens remained low. Water age, and the corresponding physicochemical changes, strongly influenced microbial abundance and community composition. Differential initial microbial colonization also had a lasting influence on microbial communities in each reactor (i.e., historical contingency).

COVID-19 大流行期间非住宅用水需求的减少凸显了了解水龄如何影响管道分配系统中的饮用水质量和微生物群的重要性。使用台式模型分配系统，我们旨在表征水龄升高对散装水和管壁生物膜中微生物群的影响。五个复制恒流反应器在建筑物关闭前 6 个月和关闭后 7 个月内使用市政氯胺自来水。建筑物关闭后，进入反应器的氯胺含量下降；在反应器的大量水和生物膜中，平均细胞计数和 ATP 浓度增加了一个数量级，而机会性病原体的检测率仍然很低。水龄和相应的物理化学变化强烈影响微生物丰度和群落组成。不同的初始微生物定殖也对每个反应器中的微生物群落产生持久影响（即历史偶然性）。