Reduce the risk of Legionella in your building

Blog Post
At the Portland Water Bureau, public health is our highest priority. We are sharing this information so you can take steps to protect the health of people in your building.

Legionella risk

Legionella is a potentially harmful bacteria that can grow in water that is warm and stagnant. Legionella poses a health risk because it can cause a serious illness called Legionnaires’ disease if it is inhaled into the lungs as a mist or aerosol.

In buildings, devices such as faucets, showers, cooling towers, hot tubs, and decorative fountains can form mists or aerosols that spread Legionella. It’s important to note that people cannot develop Legionnaire’s disease by drinking tap water – the bacteria must be inhaled.

Graphic about water safety that reads: Steps managers of large buildings should take to maintain water quality. 1. Run water at least weekly 2. Maintain hot water at or above 140 degrees farenheit. Make sure your plumbing is working properly 4. Maintain building water treatment  systems 5. Follow CDC water management plan recommendations.

Legionnaires’ disease is the number one cause of waterborne disease in the United States. Common symptoms include cough, shortness of breath, fever, muscle aches and headaches. Symptoms usually begin two to 14 days after exposure, but it can take longer. People with lung or respiratory conditions may be more vulnerable to the symptoms, resulting in prolonged illness, even death. For more information, visit and search for “Legionella.”

The COVID-19 pandemic has changed how we use buildings. That may pose a higher risk of spreading Legionella because many buildings in Portland have used less water than normal. Using less water and letting water sit in pipes for long periods of time create conditions that increase the risk of Legionella growth.

Important steps to protect water quality and human health

  1. Identify the risks.
  • Building occupants: Think about the risks specific to the people who use your building. Anyone can be affected, but Legionnaire’s disease is more common in people who are over 50 and people with vulnerable immune systems.
  • Changes in water use: Periods of low or intermittent use can cause stagnant water and increase the risk of Legionella growth in the building.
  • Temperature: The hot water system must keep water hot and the cold water system should keep water cold. Legionella grows best in water between 77° and 108° F.
  • Potential trouble spots: Certain devices, like cooling towers, showers, decorative fountains, and hot tubs can increase the risk of spreading Legionella.
  1.  Take steps to reduce the risks.
  • Develop a water management plan for your building.
  • Regularly flush the plumbing to bring fresh, high-quality water into the building.
  • Regularly drain and clean water storage devices, water heaters, and mechanical devices, (including cooling towers and misters) according to manufacturer instructions.
  • Ensure the hot water system is set hot enough  (140º or above at the water heater) so that the water stays above 120º F throughout the building. Consider using point-of-use mixing valves to prevent scalding.
  • Ensure worker safety by using personal protective equipment (PPE).

Water quality and water management

To learn more about water quality and water management, and what you can do to reduce risks in your building, start on these Portland Water Bureau websites: 

More questions? Contact us at 503-823-4604 or

Health questions

Questions about Legionella or Legionnaire’s disease, or other communicable disease inquiries? Contact Multnomah County Health Department at 503-988-8834.