Are carbon water filters safe for private wells? Evaluating the occurrence of microbial indicator organisms in private well water treated by point-of-use activated carbon block filters

• Published in: International journal of hygiene and environmental health Vol. 238; p. 113852
• Main Authors: Mulhern, Riley, Stallard, Megan, Zanib, Hania, Stewart, Jill, Sozzi, Emanuele, MacDonald Gibson, Jacqueline
• Format: Journal Article
• Language: English
• Published: Elsevier GmbH 01.09.2021
• Subjects: Activated carbon; Drinking water; Microbial risk assessment; Point-of-use; Private wells; Private wells; Drinking water; Microbial risk assessment; Point-of-use; Activated carbon
• ISSN: 1438-4639; 1618-131X
• DOI: 10.1016/j.ijheh.2021.113852

Point-of-use (POU) water treatment is highly relevant to private well users vulnerable to chemical contamination, but uncertainty remains around the effects of activated carbon based POU devices on the microbial quality of the treated water. In this study, under-sink activated carbon block water filters were installed in 17 homes relying on private well water in North Carolina. The influent and effluent water in each home was evaluated for bacterial and viral microbial indicator organisms monthly for five months. Multiple logistic regression was used to identify water quality and water usage variables that were significant predictors of each indicator organism occurring in the filter effluent. The odds of total coliforms occurring in the effluent decreased by 84% with each 1-log10 increase in the influent HPC (p < 0.05), suggesting a protective effect by native heterotrophic bacteria, but increased by over 50 times with low cumulative water use (p < 0.05). The filters were not protective against coliphages in the influent and viral shedding may occur after periods of increased virus concentrations in the raw well water. Specific bacteria were also found to increase in the effluent, causing a shift in the bacterial community composition, although potential opportunistic pathogens were detected in both the influent and the effluent. Overall, under normal conditions of use, the filters tested in this study did not represent a significant additional risk for well users beyond the existing exposures from undisinfected well water alone. [Display omitted] •Activated carbon POU filters may not add significant microbial risk for well users•Activated carbon POU filters do not mitigate existing microbial risks in well water•Heterotrophic bacteria in well water may protect against colonization by coliforms•Frequent flushing and use are recommended to minimize colonization