Implementing Control Measures

Key points

  • Consider implementing immediate control measures if a source is suspected, including for potable water sources.
  • Potable water is a term for water used for drinking and bathing.
  • Tailor the measures to the building and outbreak.
  • Implementing immediate control measures can help reduce the risk of Legionella transmission to susceptible people.


Take measures to reduce the risk of ongoing transmission. Immediate control measures are intended to prevent exposure to systems or devices suspected to have Legionella.

Examples of immediate control measures for potable water systems include:

  • Restricting showers (using sponge baths instead)
  • Avoiding exposure to hot tubs
  • Installing point-of-use microbial filters
  • Halting new admissions
  • Temporarily closing the building, affected area, or device
  • Implementing contingency responses and corrective actionsA
  • Distributing notification letters to the appropriate audience(s)

Examples of immediate control measures for devices include:

  • Turning off devices such as cooling towers or decorative fountains
  • Restricting access to areas with devices such as hot tubs

Tailor options to the structural characteristics of the building and circumstances of the outbreak.

Point-of-use filters

Point-of-use (POU) microbial filters can be installed on any showerheads or sink/tub faucets intended for use. POU filters protect only the connected fixture. Correct location selection is critical to preventing Legionella exposure across the water system.

Select filters with an effective pore size of 0.2 microns or less that comply with the requirements of ASTM F838. Understand and follow manufacturer recommendations regarding frequency of replacement and appropriate operating conditions. Conditions refers to the temperature, pressure, and chemical levels that filters can withstand.

Confirm if filters need to be removed during acute remediation procedures.