Most RV water advice is about taste, scale, and flow. This article is about something quieter: a bacterium called Legionella that can grow in warm, slow-moving water. It matters to RVers because an RV is, in practice, a small building water system that sits unused for weeks or months, then gets turned on and used for hot showers. This guide walks through what the CDC says about Legionella, why a parked rig fits the description, and a practical routine for the first day of a trip. It is general education, not medical advice.
What Legionella is and how people get sick
Legionella is a bacterium that causes Legionnaires' disease, a serious form of pneumonia. According to the CDC overview, people can get Legionnaires' disease by breathing in mist containing Legionella bacteria, and in general it is not spread from person to person. Symptoms usually develop 2 to 14 days after exposure, though it can take longer, and include cough, fever, headaches, muscle aches, and shortness of breath. The CDC also notes that most healthy people exposed to Legionella do not get sick, but certain factors raise the risk.
The CDC's page on how Legionella spreads says inhaling water droplets small enough to breathe in is the most common way people get sick. Less commonly, it happens through aspiration, when water accidentally goes into the lungs while drinking. That is why the concern centers on showers, faucets, and anything that turns water into a fine mist, rather than on the water you simply drink.
Why a parked RV fits the description
The CDC lists several conditions that help Legionella survive and grow in building water systems. Three of them describe a stored RV closely:
- Warm temperatures. The CDC gives 77 to 113°F (25 to 45°C) as the range most favorable to growth, and notes that Legionella may grow at temperatures as low as 68°F (20°C). A closed-up RV in a warm climate can sit in that range for days.
- Slowly moving or stagnant water. The CDC lists this as a condition that helps Legionella grow. Water that has sat in your lines, pump, and water heater all off-season is the definition of stagnant.
- Biofilm. The CDC describes biofilm as slime that provides a place for germs to grow, and says Legionella can live and grow in it. Its potable water guidance lists sediment and biofilm among the key factors, along with temperature, water age, and disinfectant residual.
The CDC's toolkit for potable water systems is written for commercial and institutional buildings, not RVs, so treat the numbers below as the reference point that guidance uses rather than as an RV-specific standard. Your RV's manuals come first.
The temperature picture
For building plumbing, the CDC toolkit recommends keeping cold water below the favorable growth range of 77 to 113°F, storing hot water above 140°F (60°C), and keeping circulating hot water above 120°F (49°C). A separate CDC page for vacation rental owners says to set a property's water heater at or above 120°F to minimize Legionella growth. The same page notes that 130 to 140°F can kill many harmful germs but also increases the scalding risk, and advises thermostatic mixing valves at the faucet or shower if the heater is set above 120°F.
Two cautions apply to RVs. First, look up your water heater manufacturer's instructions before changing any setting. Second, scalding is a real hazard, and the CDC itself flags it. A hotter heater is not automatically a better answer. Cold-water temperature is harder to control in a rig sitting in the sun, which is another reason flushing matters.
A first-day routine for a stored or idle RV
The CDC's guidance for vacation rentals gives a simple rule: if faucets or showerheads have not been used for a week or more, flush them shortly before guests arrive. That maps neatly onto an RV that has been parked. Here is a practical adaptation.
- Start with your normal fresh-water process. If the system was winterized or stored, follow your de-winterizing and sanitizing steps first. Our guides on flushing and sanitizing the fresh water tank and spring water system startup cover that.
- Open every faucet, hot and cold. Kitchen, bath, outdoor shower, and any other outlet. Run each until the water looks and smells normal. Do the shower last and keep your head out of the spray while it purges.
- Flush the water heater according to the manufacturer's instructions. The CDC says to routinely flush the water heater according to manufacturer recommendations. Our article on RV water heater maintenance covers the mechanics.
- Inspect the end points. The CDC says faucets and showerheads can be a problem if they are not used regularly or have not been replaced or cleaned in a long time, with visible buildup on aerators as an example. Unscrew aerators, look, clean or replace.
- Check your filter housings. The CDC toolkit lists filters among components to clean and maintain regularly. Replace cartridges on schedule and sanitize canisters when you service them. See cleaning and sanitizing filter housings.
- Repeat the flush after any long gap. A week or more of non-use is the CDC's trigger.
Where filters fit, and where they do not
It is easy to assume that a water filter is a Legionella solution. It is not, and nothing in the CDC guidance says so. A sediment or carbon filter is designed to improve taste and remove particles or chlorine, and the CDC lists disinfectant residual as one of the factors that influence Legionella growth. Our reading of that is a reasonable caution rather than a CDC statement: if a carbon filter removes the chlorine that a municipal supply carries, the water downstream of it no longer has that disinfectant, so the stagnant plumbing after the filter depends on you flushing it. A filter housing that holds water for weeks can also become a place for slime to build, which is why the CDC's maintenance advice includes filters.
If you want to know what a filter is certified to do, check the label and verify the claim. Our guides to verifying an NSF certification claim and reading your filter label explain what those claims do and do not cover. For Legionella specifically, the controls the CDC emphasizes are temperature, water age, flushing, and cleaning, not a particular filter.
Who should be extra careful
The CDC says certain factors put people at increased risk for Legionnaires' disease, and points readers to its risk factors page for the specifics. If anyone traveling with you has a weakened immune system or a chronic lung condition, or if you are unsure whether you fall into a higher-risk group, ask your doctor before relying on a general checklist. If someone develops a cough, fever, or shortness of breath within about two weeks of travel, tell their clinician about the RV and any hot tub or shower use, since the incubation period can be that long.
Quick reference
- The CDC growth range is 77 to 113°F, with growth possible as low as 68°F.
- Stagnant water, biofilm, and warm temperatures are the conditions to avoid.
- Flush faucets and showerheads that have sat for a week or more.
- Flush the water heater per the manufacturer, and clean aerators, showerheads, and filter housings.
Bottom line
Legionella is not a reason to stop RVing or to fear every shower. It is a reason to treat a parked rig like what it is: a small water system with long idle periods, warm weather, and plenty of surfaces for biofilm. A thorough flush at the start of the season and after any long gap, plus regular cleaning of aerators and filter housings, matches what the CDC recommends for buildings and costs almost nothing.
Questions about sanitizing steps or a filter setup for your rig? Call us at 833-FIXED-RV or browse the rest of the RV Water Filter Store blog.
