Legionella
EPA Limit (MCL)
No MCL
Health Goal (MCLG)
Zero (0)
No level is considered safe
Unit of Measure
presence/absence
How concentrations are reported
No enforceable MCL; regulated through treatment technique requirements under the Surface Water Treatment Rule. CDC estimates 10,000-18,000 hospitalizations per year.
Health Effects
Legionnaires' disease: severe pneumonia with fever, cough, and shortness of breath. Pontiac fever: milder flu-like illness.
The EPA has set the health goal (MCLG) at zero, meaning no level of exposure is considered risk-free.
How It Gets Into Water
Naturally found in freshwater; grows in warm water systems including cooling towers, hot tubs, plumbing systems, and decorative fountains
Official EPA Guidance
For authoritative information on Legionellain drinking water, visit the EPA's official resource page.
View EPA Guidance ↗