Preventing Legionnaires Disease>>>

By INDEX Editorial Team | Based on peer-reviewed research –

Reduce preventable risks by understanding where Legionella can grow, how water systems spread it, and which maintenance steps are appropriate for your home or building.

Legionella bacteria are found naturally in freshwater environments. They become a health concern when they grow and spread in building water systems or devices that create water droplets small enough to breathe in. That means prevention is mainly about managing water—not buying an air purifier or treating indoor air as the source. Showers, faucets, hot tubs, decorative fountains, cooling towers, and some humidifying devices can generate droplets or mist. [2]

For homeowners, practical steps include maintaining fixtures and water-using devices, paying attention to stagnant water, and following safe procedures after a period of low use. For building owners and facility managers, the central task is a documented water management program suited to the building’s systems and occupants. The Centers for Disease Control and Prevention (CDC) describes such a program as the primary strategy for controlling Legionella growth and spread. [1]

INDEX is a 501(c)(3) environmental health nonprofit. Our Science-to-Solution approach connects environmental health research with practical pathways, without presenting any product as an endorsement.

What is Legionnaires’ disease—and how does it spread?

Legionnaires’ disease is a serious type of pneumonia caused by Legionella bacteria. People most often become infected by breathing in contaminated water mist. In general, the disease does not spread from person to person. Legionella can also cause Pontiac fever, a milder illness. [5]

Most people exposed to Legionella do not become ill, but some people are at greater risk. These include adults 50 and older, current or former smokers, people with chronic lung disease, and people with weakened immune systems or certain underlying conditions. [2]

Symptoms of Legionnaires’ disease can resemble other types of pneumonia and may include cough, fever, muscle aches, headache, and shortness of breath. Confusion, nausea, or diarrhea can also occur. The CDC says symptoms typically begin two to 14 days after exposure, though it can take longer. Anyone with concerning symptoms—especially someone at increased risk—should contact a healthcare provider and mention possible exposure to a building water source. [5]

Criteria first: What should effective prevention address?

A practical prevention plan should address the conditions that allow Legionella to grow and spread, rather than rely on a single device or one-time treatment. Look for these essentials:

• Control stagnation. Water that sits unused can lose disinfectant residual and experience temperature changes. Unused outlets, low-flow areas, and capped or abandoned plumbing can contribute to stagnation.
• Maintain water-using equipment. Sediment, scale, corrosion, and biofilm can support bacterial growth. Fixtures and devices that create mist need appropriate cleaning and maintenance.
• Manage temperature and disinfectant within a system-specific plan. Building water systems vary. Temperature targets, disinfection, and safeguards must be compatible with applicable codes, scald prevention, and the building’s design.
• Reduce exposure to spray where practical. Ventilation, careful flushing, and properly maintained devices can help limit contact with water droplets.
• Use monitoring and corrective steps—not assumptions. A clear plan identifies who checks conditions, how often, what limits apply, and what to do when a limit is missed.

The CDC identifies adequate disinfection, temperature management, prevention of stagnation, and control of sediment, scale, corrosion, and biofilm as general principles of water management. [1]

How to reduce Legionella risk at home

Keep showerheads, faucets, and fixtures clean

Mineral buildup or a slimy film on a showerhead or faucet can signal that cleaning and maintenance are needed. Follow the manufacturer’s instructions for removing and cleaning a fixture; don’t mix cleaning products or use chemicals in a way that is not specified for the fixture. EPA guidance notes that keeping fixtures clean may help reduce bacterial growth and the amount of spray or small droplets. [2]

When showering, consider using an exhaust fan or opening a window if practical. This is not a substitute for maintaining the water system, but it can help remove moisture and droplets from the room. People at higher risk may want to ask a healthcare provider or local public health professional about additional precautions.

Take care when flushing little-used outlets

After time away, remodeling, or another period of low water use, stagnant water may remain in plumbing. EPA suggests considering weekly flushing for outlets that are rarely used or have been unused for an extended time. Its home guidance describes running cold water for about two minutes, then hot water until it reaches its maximum temperature. It also advises minimizing splashing and spray, using an exhaust fan or opening a window when possible, and stepping away from the outlet. [2]

Advice can differ by circumstance and public-health authority. For example, New York State advises running faucets on low and avoiding splashing after outlets have been unused for three or more days, after plumbing work, or following a boil-water notice. [3] Follow local public-health instructions when they apply. If a whole home has been unused, or you are unsure how to flush a complex plumbing system safely, ask a qualified plumbing or water-management professional for guidance.

Flushing is not a universal fix for a contaminated or complex system. A 2024 study of one aging residential building found that water flushing could reduce measured Legionella at outlets in the short term, but effects and longer-term control varied. The study’s authors emphasize the need to understand building characteristics and implement water management, rather than treating flushing as a stand-alone solution. [4]

Don’t raise water-heater temperature without considering scald risk

Water temperature is one factor in Legionella management, but turning up a home water heater can create a serious scald hazard—especially for young children, older adults, and people who cannot quickly respond to hot water. EPA advises checking local code and considering scald protection before increasing a household water-heater setting. It also notes that thermostatic mixing valves may help manage scald risk when installed appropriately. [2]

Do not apply a building-scale temperature or “shock treatment” procedure at home based on an online article. Ask a licensed plumbing professional or local health department about the right approach for your system and household.

Maintain humidifiers, filters, and other water-using devices

Humidifiers, nebulizers, and other devices that create spray or small droplets should be cleaned and maintained according to their instructions. For medical equipment such as CPAP or nebulizer devices, use the type of water and cleaning procedure specified by the manufacturer and your healthcare provider. EPA specifically notes that point-of-use filters require regular maintenance and replacement according to the manufacturer’s directions; a neglected filter is not a dependable safeguard. [2]

If you have a hot tub or spa, follow its maintenance instructions and local public-health requirements. CDC recommends proper operation and maintenance of public hot tubs as part of Legionella control; users can ask the operator how water quality is monitored and how the tub is cleaned. [6]

What homeowners can ask in an apartment or shared building

If you live in a multifamily property, you may not control the building’s water heater, plumbing circulation, cooling towers, or other shared equipment. Ask the property manager or building owner:

• Does the building have a water management program?
• Who is responsible for implementing and documenting it?
• How are little-used outlets and water-using devices maintained?
• What is the building’s procedure after a water interruption, plumbing work, or extended vacancy?
• Who should residents contact if they notice persistent stagnation, unusual conditions, or a maintenance concern?

EPA recommends asking whether a building operates a water management program when residents or occupants do not control the water system. [2] A tenant should not attempt to disinfect shared plumbing or change building water temperatures independently.

Prevention for facility managers and building owners

Hospitals, long-term care facilities, large buildings, and buildings serving people at increased risk may need a program covering the entire building. Smaller buildings may need a program for particular devices, such as cooling towers, decorative fountains, or hot tubs. The appropriate scope depends on the building’s water systems, uses, location, and occupants. [1]

The CDC outlines seven core steps for a Legionella water management program:

• Establish a team responsible for the program.
• Describe the building’s water systems.
• Identify locations where Legionella could grow and spread.
• Decide where to apply control measures and how to monitor them.
• Establish corrective actions for when limits are not met.
• Confirm the program is operating as designed and is effective.
• Document and communicate program activities. [1]

This is an ongoing management process—not simply a written plan kept on file. Assign responsibility, keep monitoring records, and define what happens when results fall outside established limits. Consult the CDC’s water management toolkit and review applicable regulations, building codes, and industry guidance. ASHRAE Standard 188 sets minimum requirements for Legionellosis risk management in building water systems. [7]

Plan carefully for shutdowns and reopening

A building that has been vacant or operating at reduced occupancy may have standing water and changed disinfectant levels or temperatures. Before normal operation resumes, facility teams should assess the water system and follow a building-specific flushing, cleaning, and water-quality plan—not assume that running taps briefly resolves every risk. CDC provides specific guidance for reopening buildings after prolonged shutdown or reduced operation. [8]

The 2024 study of a highly colonized aging residential building illustrates why professional management matters: one-time heat or chemical shock treatments did not provide consistent long-term control in that specific building, while the study assessed sustained treatment under building-specific conditions. These findings should not be generalized into do-it-yourself treatment instructions. They reinforce that remediation requires qualified expertise, monitoring, and a plan tailored to the system. [4]

Common questions about preventing Legionnaires’ disease

Can I prevent Legionnaires’ disease by using an air purifier?

An air purifier does not address Legionella growing in plumbing or water-using equipment. The main prevention focus is water-system management and reducing exposure to contaminated water mist. [2]

Is Legionnaires’ disease spread by drinking water?

Most infections occur when someone breathes in water mist containing Legionella. A less common route is aspiration—when contaminated water accidentally enters the lungs. If you have a specific exposure concern, consult a healthcare professional or local health department. [2]

Can I test my home’s water myself?

A household test or a temperature reading alone cannot establish that a water system is free of Legionella. Building-level investigation and sampling require a suitable plan and qualified interpretation. If there is a known concern, contact your local health department, a healthcare provider, or a qualified water-management professional.

Does running a faucet once eliminate the risk?

No single household action can guarantee prevention. Flushing may help replace water that has been sitting in a pipe, but its effectiveness depends on the system and situation. In complex buildings, CDC recommends a full water management program with monitoring and corrective actions. [1] [4]

A practical next step

For homeowners, begin with fixture and device maintenance, safe procedures for little-used outlets, and a conversation with a qualified professional when the plumbing system or scald risk makes the right action unclear. For facility teams, review your water management program, confirm roles and monitoring records, and make a documented plan for shutdowns and reopening.