The Maine Center for Disease Control and Prevention says tests indicate chlorine eliminated the bacteria responsible for Legionnaires' disease from the Orono-Veazie Water District.
Chlorine was added after the CDC discovered the presence of the bacteria last month while investigating a cluster of six Legionnaires' cases in the Bangor area.
The CDC said the water remained safe because the bacteria levels were so low.
Legionnaires' disease is a severe form of pneumonia caused by inhaling water droplets containing the bacteria. The Legionella bacterium is common in streams and ponds but can also spread in buildings through air conditioning systems, hot tubs and fountains.
None of the six cases is linked to the water district, and the investigation into the source of bacteria is continuing. All six patients were hospitalized and one died.