Legionella – Information for Waterworks Owners


The U.S. Environmental Protection Agency (EPA) has not established a Maximum Contaminant Level for Legionella in drinking water and does not require analysis for Legionella.  The EPA’s Guidance Manual For Compliance With The Filtration And Disinfection Requirements For Public Water Systems Using Surface Water Sources states that:

treatment requirements for disinfection of a municipal water supply are thought to provide at least a 3 log reduction of Legionella bacteria. However, some recontamination may occur in the distribution system due to cross connections and during installation and repair of water mains. It has been hypothesized that the low concentrations of Legionella entering buildings due to these sources may colonize and regrow in hot water systems.

Maintaining a satisfactory disinfectant residual throughout the distribution system is crucial to controlling Legionella bacteria and associated biofilms. The disinfectant residual necessary to control Legionella may be higher than the regulatory minimum, and disinfectant residuals within buildings may be much lower than disinfectant residuals within the distribution system. Waterworks Owners are encouraged to work with building owners to determine the disinfectant residuals required to control Legionella in large or high risk facilities.

The EPA has established a Maximum Contaminant Level Goal (MCLG) of zero organisms for drinking water.  An MCLG is a non-enforceable guideline based solely on an evaluation of possible health risks, taking into consideration a margin for public safety.

If a waterworks chooses to perform Legionella analysis, the Centers for Disease Control and Prevention has published Sampling Procedure and Potential Sampling Sites offers Legionella sampling and analysis guidance.  Additional Legionella resources for waterworks can be found at the AWWA Legionella Resource Community.

For more information on Legionellosis,  which is the disease caused by Legionella bacteria, please visit the VDH Legionellosis landing webpage.