Disinfection residuals in drinking water protect water quality and public heath by limiting planktonic microbial regrowth during distribution. However, we do not consider the consequences and selective pressures of such residuals on the ubiquitous biofilms that persist on the vast internal surface area of drinking water distribution systems. Using a full scale experimental facility, integrated analyses were applied to determine the physical, chemical and biological impacts of different free chlorine regimes on biofilm characteristics (composition, structure and microbiome) and water quality. Unexpectedly, higher free chlorine concentrations resulted in greater water quality degredation, observable as elevated inorganic loading and greater discolouration (a major cause of water quality complaints and a mask for other failures). High-chlorine concentrations also reduced biofilm cell concentrations but selected for a distinct biofilm bacterial community and inorganic composition, presenting unique risks. The results challenge the assumption that a measurable free chlorine residual necessarily assures drinking water safety.

饮用水中的消毒残留物通过限制分配过程中的浮游微生物再生来保护水质和公共健康。然而，我们没有考虑这些残留物对存在于饮用水分配系统巨大内表面积上的普遍存在的生物膜的后果和选择压力。使用全尺寸实验设施，应用综合分析来确定不同游离氯状态对生物膜特征（组成、结构和微生物组）和水质的物理、化学和生物影响。出乎意料的是，较高的游离氯浓度会导致水质恶化，可观察到无机负载升高和变色（水质投诉的主要原因和其他故障的掩饰）。高氯浓度也降低了生物膜细胞浓度，但选择了独特的生物膜细菌群落和无机成分，呈现出独特的风险。结果挑战了这样的假设，即可测量的游离氯残留量必然确保饮用水安全。