Learn About Preventing Legionnaires Disease At Home

Understanding Legionnaires Disease and How It Spreads

Legionnaires disease is a serious lung infection caused by a bacterium called Legionella pneumophila. This bacterium grows in warm water environments and spreads through the air when contaminated water becomes aerosolized—meaning it turns into tiny droplets that people breathe in. Unlike some diseases spread through person-to-person contact, Legionnaires disease comes from environmental water sources, not from other infected people.

The disease was first identified in 1976 after an outbreak at a Philadelphia hotel where 221 people became ill and 34 died. The source was traced to the building's air conditioning cooling tower. Since then, public health authorities have learned that Legionella bacteria live naturally in water but become dangerous when conditions allow them to multiply to high levels.

According to the CDC, between 8,000 and 18,000 people are hospitalized with Legionnaires disease each year in the United States, though the actual number may be higher due to underdiagnosis. The disease is more common in warm months and in older buildings with complex water systems. Symptoms typically appear 2 to 10 days after exposure and include high fever, cough, chills, muscle aches, and shortness of breath. Some people also experience headache, diarrhea, and nausea.

People over 50 years old, smokers, and individuals with weakened immune systems face higher risk of severe illness. However, anyone can contract the disease with sufficient exposure to contaminated water. Understanding where Legionella grows in your home and how to prevent its growth is the first step in protecting your household.

Practical Takeaway: Legionnaires disease develops when Legionella bacteria in warm water environments are inhaled as aerosol droplets. Learning about your home's water systems helps you identify where this bacterium might grow and what conditions support its development.

Identifying Water Systems and Risk Areas in Your Home

Your home contains several water systems where Legionella bacteria could potentially grow. The most common locations are hot water tanks, hot water pipes, and fixtures that produce water spray or mist. Identifying these areas is essential because Legionella thrives in warm water—typically between 77 and 113 degrees Fahrenheit, with peak growth around 104 degrees Fahrenheit.

Hot water heaters are a primary concern because they maintain water at temperatures that support bacterial growth, particularly if the thermostat is set below 140 degrees Fahrenheit. Pipes connected to hot water systems, especially if they have sediment buildup or low water flow, create conditions where bacteria can multiply. Showerheads and faucet aerators are notable risk areas because they aerosolize water—turning it into mist that can be inhaled directly into the lungs.

Other water systems to consider include humidifiers, particularly those using hot water; air conditioning units with water systems; hot tubs and spas; decorative fountains; and any other devices that heat water or create water spray. Even small items like electric kettles used to fill humidifiers can be involved if the water sits and becomes warm.

Stagnant water—water that sits unused for extended periods—is particularly risky because bacteria have time to multiply without being flushed away. If you have a second home, vacation property, or any plumbing fixtures that go unused for weeks or months, those areas warrant special attention. Similarly, buildings with complex plumbing systems, dead legs (pipes that extend beyond where water actually flows), or areas with low water pressure create ideal conditions for bacterial growth.

Practical Takeaway: Walk through your home and note all water systems, particularly those that heat water, produce spray or mist, or may sit unused. Pay special attention to hot water heaters, showerheads, humidifiers, and decorative fountains as these are common sources of aerosolized water exposure.

Maintaining Safe Hot Water Temperatures

The most effective way to prevent Legionella growth is maintaining hot water at temperatures high enough to kill the bacteria or prevent its multiplication. The CDC recommends maintaining hot water heater thermostats at 140 degrees Fahrenheit (60 degrees Celsius) or higher. At this temperature, Legionella bacteria cannot survive. Water delivered to outlets should reach at least 131 degrees Fahrenheit (55 degrees Celsius).

To check your hot water heater temperature, locate the thermostat dial on the side of your tank. Many residential tanks have a dial marked with temperature increments. If you cannot read the temperature directly, use a reliable thermometer to measure water temperature at the hot water tap nearest to the heater. Run the hot water for several minutes before measuring, as initial water in the pipe may be cooler than the stored water.

Setting water heater temperatures too low—often done to reduce energy costs or prevent scalding—creates an environment where Legionella thrives. However, water hotter than 140 degrees Fahrenheit can cause severe burns, particularly in young children and elderly people. Some homes address this concern by maintaining the tank at 140 degrees while installing anti-scald devices at individual showerheads and faucets to reduce water temperature at the point of use.

For people with young children, elderly family members, or individuals with reduced sensation to temperature, working with a licensed plumber to install anti-scald mixing valves is one option. These valves automatically reduce hot water temperature at specific outlets while maintaining the higher temperature in the storage tank. This approach provides protection against both Legionella growth and scalding injuries.

If you have a vacation home or property left vacant for extended periods, draining the hot water tank or maintaining it at 140 degrees Fahrenheit is important. Some people turn off heating systems in unused properties to save money, but this allows Legionella to grow. If you anticipate vacancy, consulting with a plumber about temporary temperature maintenance or tank draining is worthwhile.

Practical Takeaway: Check your hot water heater thermostat and adjust it to maintain at least 140 degrees Fahrenheit. Use a thermometer to verify the temperature at your tap. If you have concerns about scalding, discuss anti-scald mixing valves with a plumber as an alternative to lowering the overall tank temperature.

Cleaning and Maintaining Water-Using Fixtures

Regular cleaning of fixtures that spray or aerosolize water reduces the likelihood of Legionella exposure. Showerheads, faucet aerators, and any removable components should be cleaned monthly or more often if you notice sediment, mineral buildup, or discoloration. These deposits can protect bacteria from disinfectants and provide nutrients that help them grow.

To clean showerheads, unscrew them from the pipe and soak in white vinegar for 1 to 2 hours. This dissolves mineral deposits. Use an old toothbrush to scrub the small holes where water exits. Rinse thoroughly with clean water before reattaching. For aerators on faucets, use the same approach. If buildup is heavy, soaking overnight may be necessary.

Some people prefer replacing showerheads and aerators rather than cleaning them, particularly if they are heavily corroded or several years old. New, inexpensive replacements are readily available at hardware stores. When replacing fixtures, choose those with lower flow rates when possible—high-velocity spray creates more aerosolization and greater inhalation risk.

Humidifiers require particular attention because they intentionally create water mist. If you use a humidifier, empty the tank daily rather than letting water sit. Wash the tank with hot soapy water and dry it completely. Use distilled or demineralized water rather than tap water, as this reduces mineral buildup that can harbor bacteria. Some humidifier manufacturers recommend adding a small amount of white vinegar or hydrogen peroxide to the water tank, though following your specific humidifier's instructions is important.

Hot tubs and spas require regular maintenance including proper chlorination or other disinfection, maintaining water temperature below 104 degrees Fahrenheit when not in use, and following manufacturer guidelines for drain and cleaning cycles. If you will not use a hot tub for an extended period, draining it completely prevents bacterial growth.

Check exposed hot water pipes for leaks that could create small water spray or mist. Even minor drips can aerosolize water. Pipe insulation helps maintain water temperature and prevent condens