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 world-wide in low numbers in natural freshwater bodies. Drinking water providers 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 very 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 for Disease Control and Prevention (CDC).

Think you are sick from Legionella? Please consult with your healthcare provider or contact the Multnomah County Health Department at 503-988-8834.

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 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 began voluntary 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 steps to reduce the growth of Legionella in your living spaces. Follow guidance in the CDC’s Toolkit for Controlling Legionella in Common Sources of Exposure. This toolkit provides step by step actions you can take to help reduce the risk associated with Legionella in your living spaces, including from hot tubs, humidifiers, medical equipment, and ice machines.