Legionella and drinking water

Learn about Legionella, what the Water Bureau is doing to protect public health, and steps everyone can take to prevent Legionella growth in their plumbing systems.
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Water quality in home and building plumbing

Public health is our highest priority. We are responsible for delivering high-quality drinking water to your home and take steps to make sure your water is safe to drink. However, we can’t control water quality once it enters your home or building. We rely on you to be our partner in maintaining the water quality in your home or building to ensure your water stays safe at the tap. On this page, you will find actions you can take to protect your health and limit microbial growth in your plumbing system.

Legionella information for large building managers

About Legionella and Legionnaires' disease

Legionella, the bacteria that causes Legionnaires' disease, is found across the country in low numbers in natural freshwater bodies. Drinking water systems are required to treat the water to control Legionella in drinking water and protect public health. When water quality is not maintained in buildings, Legionella can also be found in building plumbing systems, decorative fountains, and evaporative cooling systems, like cooling towers, and can make people sick. Legionella is the most common cause of waterborne disease in the United States.

Healthy people are at lower risk for getting sick from Legionella. People most at risk for getting sick from Legionella and contracting Legionnaires’ disease are people over 45 and have other medical conditions or an impaired immune system. People get sick from Legionella by breathing in small water droplets containing the bacteria, such as breathing shower steam or mist from a decorative fountain. Legionnaires' disease is not known to spread from person to person or from drinking the water. Learn more about Legionnaires' disease from the Centers of Disease Control and Prevention (CDC).

The risk of getting sick from Legionella in a single-family home is relatively low. Large buildings that have complex plumbing systems are at a much greater risk of Legionella growth. However, everyone can take steps to prevent Legionella growth in their plumbing systems.

How the Portland Water Bureau manages Legionella

The EPA and Surface Water Treatment Rule requires drinking water systems to take steps to reduce illnesses caused by microorganisms in drinking water. Like other water providers around the country, Portland Water Bureau controls these microorganisms, which includes Legionella, E. coli, and Giardia lambia, by treating our drinking water with chlorine. Our certified staff maintain and operate the drinking water system to maintain adequate levels of disinfection as the water moves through our drinking water pipes and into your home or building.

In 2021, the Portland Water Bureau started testing for Legionella throughout the city. In partnership with our public health partners, we voluntarily began testing for Legionella to monitor for it in the water that is delivered to homes and businesses. Legionella has not been detected in this routine testing.

Steps all residents can take

Whether you own or rent the space you live in, you can take the following steps to reduce the growth of Legionella in your living spaces.

Maintain the hot water system

Drawing of a cross-section of a hot water heater tank.

If you have access or control of your water heater, follow the steps below under Maintaining your water heater.

If you live in a care facility or apartment building, your property manager or landlord is responsible for maintaining the hot water system. If you have concerns about Legionella exposure in your building, check with your property manager to see if they have an active water quality management plan to reduce the risk of Legionella growth.

Clean showerheads and faucets

shower head with water coming out

Legionella can grow in biofilms in your showerheads and faucets. Cleaning showerheads and faucet aerators at least four times per year can minimize the growth of Legionella bacteria. To clean them:

  1. Disassemble the showerhead and hose that is attached to it.
  2. Wipe clean any biofilm or debris buildup.
  3. Place the fixture in a bucket filled with vinegar or chlorine bleach. Let it soak for a few minutes to remove any deposits.
  4. Rinse with fresh water and reassemble.

Maintain humidifiers

White steam is billowing from a circular humidifier.

If not cleaned properly, a humidifier can host Legionella bacteria and transport it to your lungs through its fine mist of water. Regularly clean your humidifier per the manufacturer's instructions to keep it free of bacteria. Also, only fill your humidifier with distilled water or water that you boiled for one minute and then let cool down. Boiling the water protects you from any bacteria that may be in your plumbing system.

Maintain hot tubs

A circular, inground hot tub that is bubbly and fizzy with green and blue water.

Legionella grows best in warm water, like the water temperatures in hot tubs. But warm temperatures also make it hard to keep disinfectants at the levels needed to kill germs like Legionella. Therefore, hot tub owners or facility managers must ensure they are operated properly and adequately cleaned. If you have or maintain a hot tub:

  • check the amount of disinfectant in the water and the pH twice a day
  • have a regular cleaning schedule to scrub away slimy films or algae from the sides of the tub
  • replace filters in accordance with the manufacturer's specifications

See the CDC guide on Controlling Legionella in Hot Tubs.

Replace water filters

drawing of two hands installing a white, cylindrical water filter on the end of a kitchen faucet.

People do not get sick from Legionella by drinking the water it lives in. Using a water filter for drinking water will not reduce your risk of contracting Legionnaires' disease. If you do use a water filter for your drinking water, change and maintain the filter according to the manufacturer's recommendations. If the filter is not maintained properly, Legionella bacteria can grow on the filters and lower the water quality. If you are at high risk of getting a severe illness from Legionella, have someone else change your water filter or take safety precautions before changing the filter yourself.

If you can't set your water heater temperature and are concerned about Legionella exposure in the shower, consider installing a shower filter. Various filters are available for purchase online. Shower filters should always be changed according to the manufacturer's instructions.

Maintaining your water heater

Set the water heater temperature

If your water heater has a tank, set your heater to 140 degrees Fahrenheit to reduce the growth of Legionella. To better reduce Legionella growth, the temperature leaving the faucet should be at or above 120 degrees F. However, this is very hot and can scald (burn) skin, especially for children and the elderly. To help prevent scalding, you can install point-of-use mixing control the water temperature at the showerhead or faucet. Contact a plumber if you don't know how to do this.

Electric versus gas or oil water heaters

Electric water heaters have a heating element that sits slightly above the bottom of the heater. This creates a layer of cooler water at the bottom of the tank that can be the perfect temperature for Legionella growth. If your home has an electric water heater, consider setting the temperature to 140 degrees Fahrenheit or above to make sure growth of Legionella is minimized.

Gas and oil water heaters heat from the bottom up and do not have layers of cooler water at the bottom.

Flush the water heater tank

It isn't always possible to drain your water heater tank. But, if possible, this can help replace stagnant water that can harbor Legionella. Emptying and refilling (flushing) the water tank is a good practice. You can hire a plumber to do this for you. Completely flush (empty and refill) your water heater:

  • when you return after a week-long or more vacation
  • before you move into a home
  • after plumbing work
  • if your hot water is discolored

Steps to flush your water heater tank:

  1. Turn off the gas or electricity to the water heater.
  2. Open a hot water faucet in the home and run the water for about 10 minutes to reduce the water temperature in the tank.
  3. Attach a garden hose to the existing drain valve and route it to a floor drain.
  4. With the cold water valve open to drain the tank, open the drain valve. Please use caution, as sediment can build up within the water tank and can clog the drain line or valve. Follow the manufacturer's procedure for restarting your hot water heater.