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Ground Water and Drinking Water


Legionella bacteria can be found throughout the world, mostly in aquatic and moist environments (e.g., lakes, rivers, ground water and soil). Legionella can adversely impact public health. CDC estimates that 8,000 to 18,000 people are hospitalized with Legionnaires’ disease each year in the U.S.

Where has Legionella been found?

Legionella bacteria are found naturally in the environment worldwide, usually in aquatic environments. The bacteria also occur in distribution systems and premise plumbing.

How are people exposed to Legionella?

  • People are exposed to Legionella when they inhale water droplets containing the bacteria.
  • Legionella can grow in water systems in the premise plumbing of:
    • large buildings (consisting of hot water heaters, storage tanks and pipes)
    • cooling towers
    • decorative fountains
    • hot tubs

What are the health effects from exposure to Legionella ?

Legionellosis is a respiratory disease caused by Legionella bacteria. Sometimes the bacteria infects the lungs and can cause a severe pneumonia called Legionnaires' disease. The bacteria can also cause a less serious infection that seems like a mild case of the flu called Pontiac fever. For more information please visit:

Who can get Legionnaires’ disease?

Most healthy people do not become infected with Legionella after exposure. People at higher risk of getting sick are:

  • people 50 years or older
  • current or former smokers
  • people with a chronic lung disease (like chronic obstructive pulmonary disease or emphysema)
  • people with a weakened immune system from diseases like cancer, diabetes or kidney failure

What is premise plumbing?

The term “premise plumbing system” refers to the portion of the water distribution system from the water meter to the tap in homes and buildings.

What if my home is tested for Legionella in the drinking water and the test is positive?

Consult with your state and county health departments. Single-family or small multiple-family residences should follow current state, county and city guidelines for their water.