Legionella poses a minor risk for most healthy individuals. Outbreaks are usually related to the more complex plumbing systems in larger buildings rather than in a single-family home. For these reasons, homeowners should not be overly concerned about the risk of legionellosis. However, for homes with “at risk” populations, such as the elderly, those with compromised immune systems,  (link to Health Effects page) or for homeowners who would like to take additional precautions, here are some steps you can take to reduce Legionella risk.

Regular Maintenance

Regular maintenance is a simple task that, when done often, can minimize risk of Legionella. Such maintenance includes cleaning shower heads and faucet aerators. Flushing the hot water tank on a regular basis may also mitigate risk, but this should be done with caution and performed by a qualified plumber.

Cleaning Showerheads and Faucet Aerators


It is recommended that you clean showers heads and faucets four times per year, more often if there is a build-up of minerals on the head or in households with high risk individuals, such as those over 50 or with compromised immunity.

To do so:

  1. Disassemble the shower head and hose
  2. Place in a bucket with a product to remove any scale. Vinegar can work or a commercial product.
  3. Rinse with fresh water
  4. Soak in disinfectant 
  5. Rinse with fresh water and reassemble

Note: You may find that a chrome shower head may become discolored in the process. If that’s the case, you may want to consider replacing it with something more robust.

Have some spare washers available if leaks emerge upon reassembly.

Performing a hot water heater flush:

It is recommended to contact a licensed plumber to complete the following hot water tank and line flush

  1. Shut off the gas or electricity to the water heater and open a hot water faucet and run the water for about 10 minutes to reduce the water temperature in the tank.
  2. Attach a garden hose to the existing drain valve and route it to a floor drain. With the cold water value open to purge the tank, open the drain valve. Caution, sediment can accumulate within the water tank and could clog drain line or valve.
  3. Follow the manufacturer’s procedure for restarting your hot water heater.

It is recommended that the hot water heater be flushed:

  • after a one-week vacation
  • after an extended lack of use (more than one week)
  • before moving into a home
  • after minor plumbing work
  • if water becomes discolored
  • before you buy your next water heater

Maintaining Your Hot Water Heater

Legionella can multiply in your plumbing system when water temperatures are between 20-45°C oF). The bacteria are not active below 20°C and do not survive above 60°C
Therefore, hot water heaters should be set at no lower than 60°C (140°F) and distribute water at 50°C (122°F) or higher to minimize the risk of scalding, thermostatic mixer valves should be fitted as close as possible to outlets.  Where mixing valves are not available or feasible, the hot water heater temperature can be set to 50°C (122°F) to reduce the risk of scalding, particularly when children or the elderly are present in the home.  For homes, where the risk of legionellosis is already low, hot water temperatures at 50°C (122°F) are adequate.

  Figure 1

Knowing your water heater (Gas vs Electric)

Electric and gas/oil hot water heaters differ in how the water is heated and are different in the potential for growth of Legionella. Because hot water rises, electric water heaters, even set at 140oF can have water temperatures of 86 to 104oF at the bottom of the tank below the heating element (Figure 1).  Gas/oil water heaters heat the water from the bottom, so there is no zone of cooler water.  Homes with high risk individuals may consider installing tankless hot water system (set at 50°C or 122°F) which both reduces the risk of scalding and prevents the growth of Legionella.



Water Treatment and Filtration

Water filters, such as those that are installed at the kitchen faucet, can be especially useful when at risk patients are in need of additional layers of protection, as these filters can be installed at the point where water comes out of the tap. It is very important that this type of filter be changed according to the manufacturer’s recommendations because if left for prolonged periods of time, Legionella can grow on the filters and actually degrade water quality. Commercially available filters for the following items should always be changed according to the manufacturer’s instructions:

  • Showerhead and Faucet filters
  • Refrigerator and icemaker filters
  • Whole house water filters



Humidifiers create liquid droplets of water (aerosols) by design, so if they are not properly maintained they can be a mechanism for the growth and transmission of Legionella. Due to this, humidifiers must be closely examined. Humidifiers can be complex appliances that require a specialist, so it is best to get advice from the manufacturer or the supplier. Various types of humidifiers may present different levels of risk for exposure to Legionella bacteria.

  • Atomizing humidifiers or cool air humidifiers use mechanical devices or pneumatic air to create a water mist that evaporates into the air stream. These units require regular maintenance.
  • Heated pan humidifiers use a heat source to evaporate water from a pan open to the air stream but do not create water mists. Intermittent use of the device coupled with a warm pan of water may support microbial growth.
  • Direct steam-type humidifiers inject boiler-generated steam directly into the air stream. These systems do not create water mists and normally operate above 70°C (158°F), that is a temperature at which Legionella cannot survive.

Basic maintenance and sanitation is needed to ensure that your humidifier is safe and free of waterborne bacteria.

  • Daily: Empty, wipe and dry the unit. Fill with water that has been boiled and has cooled down. It is important that any water used in a humidifier be boiled and cooled, even if you are using bottled spring or distilled water, or water from filters.
  • Weekly: Thoroughly clean and disinfect the inside of the humidifier using a suitable agent (per the manufacturer's instructions), and dry.
  • Seasonally: Thoroughly clean, disinfect, and dry the humidifier before and after storage