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Does Your Water Disinfectant Matter? A New Study Thinks So

  • Writer: Everfilt® Admin
    Everfilt® Admin
  • Dec 9, 2025
  • 2 min read

Does Your Water Disinfectant Matter? A New Study Thinks So

TL;DR

A new study suggests that the stuff used to disinfect tap water, chlorine vs. monochloramine, might be linked to how often people get Legionnaires’ disease. And honestly? The difference is kind of surprising.


What’s Going On?


Researchers dug into real-world data from water utilities across the U.S. and compared it to reported cases of Legionnaires’ disease. They presented the findings at the Society for Risk Analysis meeting, and here’s the headline:


Communities using chlorine had higher rates of disease. Communities using monochloramine had lower rates. Some areas had zero cases, while others clocked in at almost 8.4 cases per 100,000 people.


That’s… a pretty big spread.


Why Would Disinfectant Even Matter?


Legionella bacteria love:


  • warm pipes

  • stale or stagnant water

  • biofilm (yes, gross pipe slime)

  • low disinfectant levels at the tap


Chlorine is great when it’s first added, but it can fade fast as it travels through miles of pipes.


Monochloramine, on the other hand, tends to:


✔ stick around longer

✔ reach the end of the plumbing system

✔ hold up better against biofilms


So instead of disinfecting mainly at the treatment plant, it keeps working throughout the system, all the way to the faucet, showerhead, or water tank.


Should Cities Start Switching?


Not so fast, this is early research, not a grand verdict.

But it does raise smart questions for:


Water Utilities


  • Maybe it’s time to look beyond “what’s cheapest”

  • Maybe “what keeps people healthier” deserves more attention


Buildings & Landlords


Even if the city water is treated well, buildings themselves can become Legionella playgrounds.


Hot water tanks + low usage + warm temps = prime real estate for bacteria.

So:


  • flush unused taps

  • maintain water temps

  • follow a building water safety plan


Regular People (aka everyone else)


Most folks are not at high risk, but it is worth knowing if you:


  • are over 50

  • smoke or used to

  • have a chronic illness

  • live in an older building


Knowledge = power. Or at least fewer bacteria.


Important: This Isn’t Fear-Mongering


Nobody is saying chlorine “causes” Legionnaires’ disease.

What this study is saying is:


The disinfectant strategy may influence risk, and that’s worth studying more.

Plus, switching disinfectants isn’t a snap decision. It affects:



But if monochloramine is doing a better job at keeping people healthy, maybe it deserves more attention.


This research is a big nudge toward rethinking water treatment.

Better disinfectant choices + better building maintenance = fewer people getting sick. It doesn’t mean panic. It does mean progress.


Sources


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