Monitoring Your Building Water

Monitoring Water Quality Parameters

The water management program team should regularly monitor water quality parameters, such as disinfectant residual and temperature levels. By monitoring these parameters, the team can ensure that building water systems are operating in a way to minimize hazardous conditions that could encourage Legionella and other waterborne pathogens to grow.

If the team finds that a control limit (e.g., temperature, disinfectant residual) is not being met, their next step will be to take corrective actions to get conditions back to within an acceptable range. Examples of chemical and physical control limits to reduce the risk of Legionella growth include:

  • Maintain hot water temperature at the highest temperature allowable by state regulations or codes (see guidance for healthcare-specific recommendations) and outside the favorable range for Legionella growth (77-113°F).
  • Ensure disinfectant levels are detectable where water enters the building and at points of use.
  • Measure the pH of the water to determine whether the disinfectant used in the building will be effective. Disinfectants work best within a narrow pH range (see parameter conditions indicating operational effectiveness).

Pay attention to patterns and trends in your water parameter measurements. Where there are concerning patterns or trends, investigate and address the underlying problem. Sometimes the solution to issues with water quality measurements may be as simple as flushing low-use areas or adjusting the thermostat on the water heater.

Routine Environmental Sampling

Routine environmental sampling for Legionella is sampling that is performed proactively as part of an effort to reduce risk of Legionella growth and transmission in building water systems (not in the context of an outbreak investigation). It is also one way to validate the efficacy of a water management program and that it is working as intended.1 The team should base decisions about routine environmental sampling for Legionella on a variety of factors. These factors include the building environmental assessment and water quality data supporting the overall performance of the water management program.  Note: The approach to routine sampling in the absence of disease may be different than the approach to environmental sampling in the context of an outbreak.

See the Routine Testing for Legionella module of the Legionella Control Toolkit for additional considerations, including a multifactorial approach to result interpretation.

Sampling Plans and Approaches

If the team decides to perform validation using environmental sampling for Legionella, they should not sample in isolation but as a part of a comprehensive water management program. The team should make specific decisions about sampling frequency, location, and methodology. Sampling plans are unique to each facility and based on factors such as:

  • Findings from the environmental assessment and any baseline Legionella test results
  • Overall performance of the water management program, trend analysis of Legionella test results, and water quality parameters (e.g., disinfectant, temperature)
  • In healthcare facilities, correlation of environmental test results with clinical surveillance data
  • Building characteristics (e.g., size, age, complexity, populations served)
  • Sites of possible exposure to aerosolized water
  • Available resources and supplies to support sampling

The team can adjust the sampling approach over time based on trend data and system changes. Organizing these data in a format that is sortable by date, location, and result can be helpful when trying to analyze trends over time. See this spreadsheet for an example of possible variables to collect and follow over time.

Taking Corrective Actions When You Find Legionella

There is no known safe level of Legionella in building water systems. Cases of Legionnaires’ disease have been associated with very low levels of Legionella in building water systems.2 The intent of a water management program should be to manage building water systems to reduce hazardous conditions that allow Legionella to grow. If the team decides to incorporate routine environmental sampling for Legionella as part of their water management program, they will need to decide how and when to respond if these bacteria are found in their water systems.

If the team finds Legionella during routine environmental sampling (in the absence of disease), CDC suggests exploring possible reasons for the growth. Corrective actions, such as adjusting temperature levels or flushing the pipes, might be sufficient. Additional actions may be necessary if there are concerning trends (e.g., persistently positive samples at a single location, positive samples in a central distribution point, positive samples in multiple points-of-use, diversity in the types of Legionella detected).


  1. Managing the risk of legionellosis associated with building water systems. ASHRAE Guideline 12-2020. Atlanta, GA: ASHRAE; 2020.
  2. Demirjian A, Lucas CE, Garrison LE, et al. The importance of clinical surveillance in detecting Legionnaires’ disease outbreaks: a large outbreak in a hospital with a Legionella disinfection system—Pennsylvania, 2011–2012Clin Infect Dis. 2015;60:1596–602.