Caution: The simultaneous invasion of trace metal pollutants in stagnant drinking water may lead to more serious microbial risks

The drinking water distribution system is the final line of defense to ensure water safety for people, however, some hidden risks may exist. Stagnation and the intrusion of trace metal pollutants are common occurrences in DWDS. In this study, a simulation of stagnant drinking water was applied to investigate the changes in water quality and microbial risks resulting from the simultaneous intrusion of trace metal pollutants under stagnation conditions, using a metagenomic approach. The differential expression of functional genes reflects the adaptive mechanisms of bacteria in response to the stress of trace metal pollutants. For the bacterial community in stagnant drinking water, Pseudomonadata is the major component. Many pathogenic bacteria have been found in stagnant drinking water, with the highest proportions being Salmonella enterica and Pseudomonas aeruginosa, which may exacerbate by the induction of trace amounts of Al. Several antibiotic resistance genes have been found in stagnant drinking water, with the highest abundance being macB, evgS, and tetA. Under the stress of trace metal pollutants, the overall exposure risk of ARGs has increased The experimental results also indicate that even the presence of trace Fe can amplify correlation of ARGs and pathogens, potentially leading to more serious hiddenly microbial risks. This study reveals the imperceptible microbial risks posed by the simultaneous invasion of stagnant and trace metal pollutants in daily drinking water and provides scientific warnings for drinking water safety.