Uncovering the Microbial Communities in Household Plumbing Systems

Household plumbing systems host a variety of generally harmless microbial life, yet the bacterial communities within homes have not been thoroughly studied. While public water utilities monitor water quality outside homes as required by the Safe Drinking Water Act, the microbial changes that occur once water enters a home are rarely examined or fully understood.

Fangqiong Ling, an assistant professor at the McKelvey School of Engineering at Washington University in St. Louis, is working with her colleagues and students to change that. They are part of a research group focused on water quality, and their study, published on December 10 in Nature Water, provides new insights into the microbial life found in household water systems.

Ling and her team conducted a seven-day sampling project, collecting data from bathroom faucets in eight households across the St. Louis metro area. They found that while the homes shared major bacterial categories, there was considerable variation at the species level from one household to another, with each home exhibiting a unique microbial signature.

"Each house has its own distinct microbiome compared to the others," said Ling.

Although public tap water undergoes strict treatment and disinfection, making the number of microbial cells detected very small, the bacteria that do survive are tough. The team found antibiotic resistance genes within these tap water microbiomes, confirming their expectations. They also observed a pattern of "resistome" across the households, where certain microbes appear to have developed resistance to common disinfectants.

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Computer modeling suggested that the establishment of microbial communities within homes occurs through both deterministic and random processes, with variations at the species level explained by factors such as random timing of microbial arrival, growth dynamics, and other factors that are still not fully understood.

The ultimate goal of this research is to develop methods for monitoring and preventing outbreaks of opportunistic pathogens or disease-spreading bacteria in households. Although such monitoring is already in development for large institutions like hospitals, it remains scarce for individual homes.

"Houses are still where most of our interactions with water occur, so we want to study the microbiomes of household plumbing systems," Ling explained.

While the study found small quantities of illness-causing bacteria in some homes, it does not necessarily indicate unsafe household water. However, Ling advocates for more public health oversight in this area.

Ling's PhD student, Lin Zhang, the lead author of the paper, has also implemented a crowd-sourcing approach by recruiting high school students as "community scientists." These students collected samples from around 100 households in the St. Louis area, and Zhang is analyzing the data for her PhD project.