Microbiological Quality of Drinking Water From On‐Demand Purified Water Dispensers in Residential Communities

On-demand purified water dispensers have been widely installed in residential communities (RCs) in China. However, water stagnation and the absence of chlorine disinfectants in these dispensers can lead to significant microbiological risks. To clarify these risks in purified water, in this study, the characteristics of the microbial community and associated microbiological hazards in 40 purified water samples from on-demand purified water dispensers in four administrative districts were investigated using quantitative PCR (qPCR) and high-throughput sequencing methods. The results revealed that the turbidity of the purified water was generally very low (< 0.28 NTU), but chlorine disinfectant was detected in more than half of the samples, indicating failure of the activated carbon process within the dispensers. Culturable bacterial counts revealed high levels of culturable bacteria in the collected water samples. Furthermore, the bacterial 16S rRNA gene copy number reached up to 6.23 Log10 Gene copies/mL. Among the seven pathogenic microorganisms detected by qPCR, Mycobacterium (95%) and Legionella (82.5%) were commonly detected with high biomass. The average gene copy number for Mycobacterium was 3.08 Log10 Gene copies/mL (0.30-4.33 Log10 Gene copies/mL), and for Legionella, it was 2.96 Log10 Gene copies/mL (0.38-4.05 Log10 Gene copies/mL). High-throughput sequencing revealed that 17 out of the top 50 microbial taxa detected at the genus level might be potential pathogens. This study demonstrates that drinking water from on-demand purified water dispensers in residential communities is associated with increased microbiological risk, necessitating enhanced monitoring and regulatory oversight.