Legionella in Drinking Water: Health Risks, Sources, and How to Remove It
Legionella is a microbial contaminant that can pose significant health risks in drinking water. Because of its potential to cause illness, the Environmental Protection Agency (EPA) has set its Maximum Contaminant Level (MCL) at 0 organisms per liter. This zero-tolerance limit reflects the acute risk associated with microbial pathogens.
Health Effects
Exposure to Legionella in water can lead to Legionnaires' disease, which is a serious, pneumonia-like illness. Because of the serious nature of this pneumonia-like disease, it is considered an acute health concern that requires prompt attention.
How Legionella Gets Into Tap Water
Legionella can enter water supplies from several distinct sources. Key sources of this contaminant include water cooling towers and hot tubs. Additionally, it is known to colonize and spread within plumbing systems.
How to Remove Legionella From Your Water
Controlling Legionella in water systems requires specific treatment methods to ensure safety. Effective strategies for managing this contaminant include temperature control, disinfection, and flushing. Applying these methods helps to reduce the presence of the pathogen in water supplies.
Should You Test Your Water?
If you are concerned about Legionella in your water, you can review your local water utility's Consumer Confidence Report or search WaterQ for local testing data. For private systems or specific building plumbing, professional testing may be recommended to verify that the water is safe from microbial contamination. You can also look up your local water system on WaterQ or check the Legionella data page for reported levels in your area.
Frequently Asked Questions
Is Legionella dangerous in drinking water?
Yes, Legionella is a dangerous microbial contaminant because it can cause Legionnaires' disease, which is a serious pneumonia-like illness. Because of the acute health risks associated with this infection, the EPA enforces a strict standard of zero organisms per liter. Prompt attention is necessary if this microbial pathogen is detected in a water system.
How does Legionella get into tap water?
Legionella can enter and multiply within plumbing systems. It is also commonly introduced from sources like hot tubs and water cooling towers.
How can I remove Legionella from my water?
Legionella can be removed or managed in water systems using temperature control, disinfection, and flushing. These treatment methods help eliminate the bacteria and keep water safe.
Source: EPA National Primary Drinking Water Regulations and WaterQ National Database. For more contaminants, visit our contaminant library.
What actually removes bacteria and e. coli
This is the one contaminant class where boiling genuinely is the right emergency answer — a rolling boil for one minute kills pathogens, and it is what a boil-water advisory is telling you to do. For a permanent fix on well water, UV disinfection is the standard. Carbon filters are worse than useless here: a saturated carbon cartridge is a warm, wet surface that bacteria colonise.
Works
- UV disinfection (NSF 55)Inactivates bacteria and viruses. Removes nothing chemical — pair with a filter.
- Reverse osmosis (NSF 58)The broadest removal available at home: arsenic, nitrate, fluoride, PFAS, TDS.
Will not fix this
- Basic activated carbon (NSF 42)
- Carbon certified for lead (NSF 53)
- Ion-exchange water softener
Test before you buy.Bacteria and E. coli can't be seen, tasted or smelled, and the right hardware depends on the concentration you actually have. A certified lab test costs a fraction of the wrong filtration system. Start with your local water quality report, and get a mail-in lab test if you're on a private well.
Options that carry the right certification
Ordered cheapest-adequate first. Prices are indicative bands and move often.
| Product | Certification | Upfront | Per year | |
|---|---|---|---|---|
| Viqua VH200 UV SystemWhole house | NSF/ANSI 55 UV disinfection.Catch:UV needs clear water to work — cloudy or iron-heavy water must be pre-filtered or the dose is wasted. | $350–600 | $80–120 | Check price |
| Home Master TMHP HydroPerfectionUnder-sink | RO plus an integrated UV stage; components tested to NSF/ANSI 58 methods.Catch:Priced for well-water households with a bacteria risk. Overkill on treated municipal water. | $500–650 | $100–160 | Check price |
| AquaTru Countertop Reverse OsmosisCountertop | NSF/ANSI 42, 53, 58, 401 and P473 certified.Catch:Takes counter space and you refill a tank by hand. Wastes some water as brine, like all RO. | $400–500 | $80–130 | Check price |
Certification listings change. Before buying, confirm the current listing for the exact model in the NSF certified products database — a manufacturer's marketing page is not a certification. WaterQ earns a commission on purchases made through these links at no extra cost to you; see our affiliate disclosure. This is general information, not medical or engineering advice.
For a full breakdown of certifications, running costs and the models worth considering, see our buying guide for bacteria and e. coli.