Flushing, Legionella and the Prevention of Legionnaires’ Disease

Flushing your water systems may be helpful in preventing Legionella growth and the risk of Legionnaires’ disease. Below are answers to frequently asked questions about Legionella and flushing.

Why is flushing used to mitigate Legionella and prevent Legionnaires’ Disease?

Flushing helps to prevent stagnation of water. Stagnant or standing water is a risk factor for the growth of Legionella and other opportunistic waterborne pathogens for the following reasons:

  • Cold water that warms to the ambient temperature may allow bacteria to grow more rapidly.
  • Hot water that cools may also reach a temperature that promotes bacterial growth.
  • Disinfectants such as municipally added chlorine may begin to drop to levels that make them less effective or ineffective.
  • Biofilm is more easily able to attach and grow in slow moving or non-moving water.

When is flushing needed to mitigate Legionella and prevent Legionnaires’ Disease?

Flushing is most often recommended when a facility has been shut down or is at low occupancy because there are no or few occupants to flush or circulate water routinely. Flushing can also be an important protocol for large facilities with that do not operate at or near 100% capacity due to natural occupancy patterns. In addition, flushing can be an important tool for facilities that are occupied by high-risk individuals such as hospitals, healthcare facilities, senior living residences, and nursing homes.

Is flushing proven to mitigate Legionella and prevent Legionnaires’ Disease?

Flushing appears to be a logical Legionella mitigation tactic based on the risk characteristics of Legionella and opportunistic waterborne pathogen growth. However, flushing should not be relied upon solely because it has not been proven effective through a peer-reviewed study. Legionella testing and other Legionella prevention measures should also be utilized as part of a comprehensive water management program.

What is the cost of flushing to mitigate Legionella and prevent Legionnaires’ Disease?

Flushing is not without cost because:

  • It results in the loss of water.
  • It can require labor costs and/or automated system equipment costs.
  • Costs may also occur if auto flushing systems are purchased and installed.

How should flushing be conducted to best mitigate Legionella and prevent Legionnaires’ Disease?

Below is a minimum recommended approach for flushing. Note that a higher frequency or longer flush time may be required for your facility.

  • Flush outlets such as sinks and showers on a weekly basis.
  • For cold water: Flush the cold water line for at least 2 minutes.
  • For hot water: Flush the hot water line until the maximum temperature is reached. Then conduct a flush for an additional 2 minutes. To ensure the maximum temperature has been reached, check and record the temperature every 30 seconds.
  • Flush storage tanks and infrequently used equipment attached to the water system once per week.

Who should I contact if I have questions about flushing to mitigate Legionella and prevent Legionnaires’ Disease?

Contact the Legionella experts at Legionella Control Systems. Given the health risk and possible high liability associated with Legionella and Legionnaires’ Disease, it is important that you consult with an experienced, independent Legionella consultant who can help you develop a Legionella prevention approach that will work and fit your budget. Nancrede has experts on staff that can help you make the best decision to protect your facility, occupants and budget.