Legionella sp. is a part of the normal ecology of a public water system and frequently detected in regulatory-compliant drinking water. Despite the consensus that preventing the proliferation of Legionella is the responsibility of building water owners and operators, water utilities may be implicated in Legionnaires’ disease outbreaks. Water utility operators are increasingly expected to have a working knowledge of Legionella within their distribution systems. This project demonstrated the implementation of a Legionella monitoring protocol; determined the occurrence of Legionella throughout the system; and evaluated any correlations with Legionella detection by gradient characteristics as well as chemical and microbiological parameters. Research Partner: Passaic Valley Water Commission. Published in 2022.