Plastic pipes are increasingly used in drinking water distribution systems, yet their impact on water quality remains insufficiently understood. Here, we systematically investigate the dual outcomes posed by plastic pipes─chemical leaching and cascaded microbial exposure risks─by integrating Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and metagenomic analysis. Our results reveal that plastic pipes continuously release dissolved organic matter (DOM), including organic additives such as bisphenols (BPs) and organophosphate esters (OPEs), which profoundly reshape microbial communities. Under chlorinated conditions, leached DOM alters microbial diversity, promoting chlorine-resistant bacteria and opportunistic pathogens (OPs), while under nonchlorinated conditions, it accelerates microbial growth and enriches antibiotic resistance genes (ARGs), OPs, and virulence factors (VFs). Among plastic materials, polyethylene (PE) exhibited the highest chemical risk, releasing high concentrations of TCPP (700 ng/L) and BPF (200 ng/L) along with 207–227 unique DOM molecules. In contrast, polyvinyl chloride (PVC) supported the highest OP abundance, while polypropylene random copolymer (PPR) fostered the greatest OP diversity. These findings challenge conventional drinking water safety assessments that separate chemical contamination from microbial risk, underscoring the urgent need for an integrated risk assessment framework. Furthermore, they highlight the necessity of paying greater attention to the chemical and cascading microbial issues arising from the leaching of plastic pipes into drinking water, and of conducting a more comprehensive assessment of the associated potential health risks.

Drinking water distribution systems are increasingly vulnerable to sewage intrusion due to aging water infrastructure and intensifying water stress. While the health risks associated with sewage intrusion have been extensively studied, little is known about the impacts of intruded bacteria and dissolved organic matter (DOM) on microbiology in drinking water. In this dynamic study, we demonstrate that the intrusion of 1 % sewage into tap water resulted in immediate contamination, including an 8-fold increase in biomass (TCC), a 48.9 % increase in bacterial species (ASVs), a 12.5 % increase in organic carbon content (DOC), and a 13.5 % increase in unique DOM molecular formulae. Over time, sewage intrusion altered tap water microbiology by accelerating bacterial growth rates (5-fold faster), selectively promoting ASVs in community succession, and producing 998 more unique DOM formulae. More significantly, statistical analysis revealed that the intrusion of 1 % sewage shifted the driving force of bacterial and DOM composition covariance from a DOM-dependent process in tap water to a bacterial-governed process post-intrusion. Our results clearly demonstrate the disruptive effects of sewage intrusion into tap water, emphasizing the urgent need to consider the long-lasting impacts of sewage intrusion in drinking water distribution systems, in addition to its immediate health risks.