Household plumbing is full of microbial life that might be a health hazard

Household plumbing systems often teem with microbial life, most of which is harmless. However, scientists have yet to fully document the bacterial communities living within people’s homes.

While the Safe Drinking Water Act ensures monitoring by public water utilities, this surveillance stops at the property line.

Once water enters a home, its microbial makeup can change significantly, evolving in ways that remain largely unmonitored and misunderstood.

Fangqiong Ling, an assistant professor of energy, environmental, and chemical engineering at Washington University in St. Louis, is conducting research to address this knowledge gap.

Together with her team, Ling aims to improve understanding of household water microbiomes and their potential implications for public health.

Household plumbing microbial communities

In a paper published in the journal Nature Water, Ling and her colleagues detailed findings from a study that sampled bathroom faucets in eight households in the St. Louis metro area.

Over a seven-day period, they tracked the flow and evolution of bacterial populations. While all houses shared major bacterial categories, there was considerable variation at the species level from one household to another.

“The houses have their own unique signature compared to the rest,” Ling explained.

Despite the rigorous treatment and disinfection protocols applied to public tap water, the researchers identified small yet resilient microbial populations.

These microbes often carry antibiotic resistance genes – a phenomenon the researchers anticipated. Using the same disinfectants across systems creates an environment where certain microbes develop resistance and form what scientists call a “resistome.”

The study revealed patterns of these resistomes across households but left questions about species-level variation unanswered.

Microbes in plumbing and public health

The researchers used computer modeling to explore how microbial communities establish themselves.

The findings suggest that both deterministic factors (such as water chemistry) and stochastic processes (random events) influence community formation. Variables like the timing of microbial arrivals, growth dynamics, and as-yet-unknown factors contribute to the observed diversity.

Ling’s work aims to anticipate and prevent outbreaks of opportunistic pathogens and disease-causing bacteria. While similar monitoring is under development for hospitals and other large institutions, individual household systems remain understudied.

“Houses are still the place where the majority of our interactions with water take place, so we want to study households,” Ling emphasized.

Though the study detected illness-causing bacteria in small quantities, this doesn’t necessarily indicate that household water is unsafe. However, Ling believes public health regulators should pay closer attention to the potential risks.

Community science and crowdsourcing data

Lin Zhang, a Ph.D. student and the lead author of the paper, led efforts to expand the study’s reach.

By involving high school students as “community scientists,” the team collected samples from about 100 households in the St. Louis metro area. These contributions are now part of Zhang’s final Ph.D. project, which analyzes household-specific microbiome signatures and their shared resistomes.

“I like that we were able to give high school students a glimpse into real-world research and the scientific method. Hopefully, this might motivate them to pursue a future in environmental engineering,” said Zhang.

The research highlights the importance of studying household plumbing microbiomes. While most bacteria are harmless, the resistance genes they carry can transfer to pathogens, especially when individuals undergo antibiotic treatments.

Understanding these dynamics is crucial, given the frequent human interaction with these microbes through daily activities like showering and cooking.

Infrastructure upgrades and future monitoring

Just a few months ago, the Environmental Protection Agency (EPA) introduced a new rule requiring municipalities to replace lead plumbing pipes within the next decade.

This infrastructure overhaul could also provide opportunities to enhance monitoring of household water systems. Beyond dealing with metals, new plumbing systems might also focus on mitigating the presence of microplastics, and better understanding microbiomes.

Professor Dan Giammar is leading projects to improve drinking water quality. He highlighted the challenges of tracking water quality changes from treatment plants to household taps.

“Aspects of drinking water quality that can change between the treatment plant and the customer’s tap have been frustratingly difficult to monitor,” said Professor Grammar.

“This innovative work provides new insights into how microbes grow and what microbes are present in premise plumbing.”

Understanding the microbiome of plumbing

Ling and Zhang’s research continues to unveil the diversity of household microbiomes. With every additional house sampled, more microbial variety emerges – presenting new questions for scientists to tackle.

Understanding the microbiome and resistome of household plumbing systems is critical for preventing health risks and improving water quality.

The collaborative efforts of researchers, students, and community scientists are paving the way for a safer, more informed approach to managing water systems in our homes.

The study is published in the journal Nature Water.

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