Legionella and Home Plumbing: What Homeowners Should Know

Legionella is a bacterium that lives in water, and the headlines it earns usually come from hotels, hospitals, and cooling towers rather than houses. That gap matters, because most of what you can read about it was written for the people who run big, complex water systems, not for someone wondering whether their own shower is a problem. For a typical home, the honest answer is that cases tied to household plumbing are uncommon, but the conditions that let the bacteria grow are real and worth understanding, and the steps that reduce them are simple and clearly safe to do yourself.

This guide stays at home scale: what Legionella is, where in your own plumbing it can grow, who in a household actually faces higher risk, and the few practical things that lower that risk without creating a different hazard. The version of this topic that covers cooling towers, large recirculating systems, and formal water-management plans belongs to commercial buildings, so see our guide on why Legionella risk matters in commercial water systems (229) for that side.

What Legionella Is and Why It’s an Inhalation Risk, Not a Drinking One

Legionella is a waterborne bacterium that causes Legionnaires’ disease, a serious form of pneumonia, when it reaches the lungs. The route is the part most people get wrong. According to the CDC, you get sick by breathing in small water droplets that contain the bacteria, not by swallowing them. As the agency puts it, water containing Legionella can spread in droplets small enough for people to breathe in.

That single fact reframes the whole problem. Drinking a glass of tap water is not the exposure people picture from the news. The risk comes from aerosols, the fine mist a fixture throws into the air. A running shower is the clearest home example, which is why showerheads come up again and again in Legionella guidance. The CDC does note one drinking-related pathway, aspiration, which happens when water accidentally goes down the wrong way into the lungs while you drink, but for healthy people the main concern remains inhaled mist rather than the water itself.

A few facts ease the worry. The CDC is clear that you can’t catch Legionnaires’ disease from another person; in general it does not spread from person to person. And home and car air-conditioning units are not a source, because they don’t use water to cool the air. The bacteria need warm water, time to multiply, and a way to become airborne, which narrows the real question down to specific spots in your plumbing.

Where It Can Grow in a Home: Tepid Tanks, Dead Legs, and Showerheads

Legionella grows when water is warm and sits still. The CDC identifies a growth range of roughly 77 to 113 degrees Fahrenheit (25 to 45 Celsius), and the same conditions that amplify it elsewhere are warm temperatures, stagnation, the scale and biofilm that coat pipes and fixtures, and the loss of disinfectant. Translate that to a house and a short list of places stands out.

A water heater that runs too cool. A storage tank held in or near that growth range becomes a reservoir rather than a barrier. The CDC’s guidance for keeping water systems safe is to set the heater high enough that stored water stays out of the danger zone, a point the next section turns into a specific homeowner trade-off.

Dead legs and rarely used fixtures. A dead leg is a stretch of pipe where water sits without moving, such as the line to a guest bathroom no one uses, a basement utility sink, or a capped stub left from an old fixture. Stagnant water there loses its disinfectant and drifts into the warm, still state the bacteria favor. The CDC flags stagnant water in plumbing as a driver of growth, and notes that when hot water sits unused, its temperature can drop into the Legionella range.

Showerheads and faucet aerators. These are where growth meets aerosol. Biofilm and scale build up inside the head and on the small aerator screen, giving bacteria a sheltered surface, and the shower then turns that water into exactly the breathable mist that matters. Buildup you can see on an aerator is a sign these surfaces have not been cleaned in a long time.

A home that sat idle. Plumbing left unused during a long vacation, or in a seasonal or vacation property, combines every risk factor at once: warm pipes, no flow, and falling disinfectant. The full routine for shutting down and restoring a vacant home’s plumbing is its own task, so see our guide on how to protect plumbing in a vacant or vacation home (129) for that procedure; here the point is simply that idle time is when home risk is highest.

Who’s Actually at Higher Risk

Most healthy people exposed to Legionella do not get sick, which is the calibration the building-focused literature often skips. The disease concentrates in specific groups. The CDC lists the higher-risk categories as people 50 years and older, current or former smokers, and people with a chronic lung disease or a weakened immune system, whether from another illness or from medication.

This is worth taking seriously without alarm. The reason to act is not that an average household faces high odds; it is that the simple precautions cost almost nothing, and the consequences for a vulnerable person are severe. Legionnaires’ disease is a pneumonia that frequently requires hospitalization. If someone in your home falls into one of those groups, the maintenance steps below shift from optional housekeeping to a sensible standing habit.

What this section is not is medical guidance. If you or someone in your household has symptoms or a specific health condition, that is a conversation for a doctor, not a plumbing article. The plumbing side of the job is to keep the water from becoming a source in the first place.

Keeping the Water Heater Hot Enough Without Risking Scalds

Here is the tension at the center of home Legionella control: the temperature that suppresses the bacteria is hot enough to burn skin. You cannot solve one problem by simply ignoring the other, so the answer is to manage both at once.

On the bacteria side, the CDC advises storing hot water at or above 140 degrees Fahrenheit to limit Legionella growth, since that keeps the tank out of the roughly 77 to 113 degree range where the bacteria multiply. On the safety side, that same hot water scalds quickly, and the agency is direct that a higher heater setting increases the scalding risk. The resolution it points to is a device, not a guess: keep the tank hot and use thermostatic mixing valves at the faucet or shower so the water reaching you is tempered down to a safe delivered temperature, around 120 degrees rather than the stored 140. The CDC also advises following state and local scald laws, which in some places set their own delivered-temperature limits.

Two cautions keep this practical and safe. First, the precise dial setting and the broader scald-prevention picture are their own topics; the water-heater temperature number and how to set it live in our guide on the right water heater temperature setting and scald safety (054), and the full set of anti-scald devices and household burn-prevention measures lives in our guide on how to prevent scalding from hot water at home (157). Treat those as the homes for the details, and treat this section as the reason the trade-off exists.

Second, know where the do-it-yourself line sits. Turning the dial on a thermostat you can reach is reasonable for many homeowners. Anything inside the heater is not. Replacing a heating element, a thermostat, a thermostatic mixing valve, or a gas component involves water-heater internals and, on gas units, a fuel line, so that work belongs to a licensed plumber rather than a weekend project. Raising the temperature without a way to temper the delivered water is the mistake to avoid, because you can trade a rare risk for a far more common one, a serious burn.

Flushing After a Vacancy and Cleaning Showerheads and Aerators

The two maintenance steps that do the most are also the two that are clearly safe for any homeowner, because neither touches a pressurized line, a gas connection, or anything inside an appliance.

Flushing clears out the stagnant water that has had time to grow bacteria and lose disinfectant. The CDC’s advice for fixtures that have gone unused for a week or more is straightforward: flush them before they are used again. In practice that means running both hot and cold water through showers, tubs, and taps, including the ones in rooms you rarely enter, until the water has fully turned over and the hot side has reached its normal temperature. The EPA recommends flushing to restore water quality after extended periods of low or no use, for the same reason: moving water out replaces it with fresh, treated water. Letting a fixture run is the whole technique. To reduce the mist you breathe while a stale shower first clears, you can point the head toward the drain and step out of the room for the first minute or two.

Cleaning attacks the biofilm and scale where bacteria shelter. Showerheads and aerators collect mineral deposits that you can often see, and removing them is routine maintenance, not a repair. You can unscrew an aerator from the faucet tip, or remove a showerhead, and soak the part in a household descaling solution such as vinegar to dissolve the buildup, then scrub and rinse it before reinstalling. Doing this periodically keeps the sheltered surfaces from accumulating in the first place. The step-by-step for clearing a clogged or scaled showerhead, if yours needs more than a soak, lives in our guide on how to clean or replace a clogged showerhead (038).

What none of this requires is opening the water heater, disassembling a valve, or chasing the problem into the walls. Home Legionella control is mostly about heat and movement: keep the stored water out of the growth range with a mixing valve handling the burn risk, and keep water moving through the fixtures and clean at the point where it turns to mist.

Frequently Asked Questions

Can you get Legionnaires’ disease from your home shower?
It is possible but uncommon. The risk comes from breathing in fine water droplets, and a shower does create that mist, so a showerhead that has grown biofilm in stagnant, tepid water is the relevant home scenario. For most healthy people the odds are low. The risk rises for people 50 and older, smokers, and those with chronic lung disease or a weakened immune system, and it rises when a shower has sat unused. Flushing unused fixtures and keeping showerheads clean address it directly.

What water heater temperature kills Legionella?
The CDC advises storing hot water at or above 140 degrees Fahrenheit to limit Legionella growth, because that keeps the tank above the roughly 77 to 113 degree range where the bacteria multiply. The catch is that water that hot scalds quickly. The recommended way to get the bacteria benefit without the burn risk is to keep the tank hot and install thermostatic mixing valves so the water delivered to faucets and showers is tempered down to a safe temperature, around 120 degrees, while following any local scald laws.

Is it safe to drink tap water that might have Legionella?
The main risk from Legionella is inhaling contaminated mist, not swallowing water, and the disease does not spread from person to person. The CDC notes one water-related pathway called aspiration, where water goes down the wrong way into the lungs while drinking, but for healthy people the central concern is aerosols from fixtures rather than the act of drinking. If you have a specific health condition, raise it with a doctor.

Do I need to test my home water for Legionella?
Routine home testing is not part of standard homeowner guidance the way the maintenance steps are, and a single test is a snapshot rather than ongoing protection. The practical approach for a household is to control the conditions: keep the water heater out of the growth range with scald protection, flush idle fixtures, and clean showerheads and aerators. If a member of your household is at higher risk or a doctor has raised the question, follow medical advice for your situation.

This article is general information, not professional or medical advice. For guidance specific to your home, water, and health, consult a licensed plumber and a medical professional.

Sources

• CDC, How Legionella Spreads: https://www.cdc.gov/legionella/causes/index.html
• CDC, Reducing the Risk of Legionella in Building Water Systems: https://www.cdc.gov/control-legionella/php/guidance/building-water-system.html
• CDC, Considerations for Vacation Rental Owners and Managers (Control Legionella): https://www.cdc.gov/control-legionella/php/hospitality/considerations-for-vacation-rental-owners-and-managers.html
• CDC, Clinical Overview of Legionnaires’ Disease: https://www.cdc.gov/legionella/hcp/clinical-overview/index.html
• EPA, Information on Maintaining or Restoring Water Quality in Buildings with Low or No Use: https://www.epa.gov/sdwa/information-maintaining-or-restoring-water-quality-buildings-low-or-no-use