Steps for flushing a building’s water system

Starting up a building’s water system after closures and sustained low use

To ensure you and your employee’s safety from both chemical and biological exposure while disinfecting and flushing the building plumping, appropriate training and PPE should be considered. You can find guidance on worker safety for Legionella control and prevention on the OSHA website.

  1. Flush the entire water system to replace all water. Use an approved chlorine testing device to measure residual chlorine, flush until measured levels are equal to or less than the supplying utility’s chlorine residuals.
  2. During flushing operate all valves in the fully open position so that any particulate matter can be flushed through. Pay close attention to float-operated or other restrictive valves which need to be manually opened to clear particulates and prevent fouling of the valves.
  3. Remove all aerator screens before flushing. Clean or replace aerator screens once cleaned to get rid of scale deposits that may contain harmful metals (lead) or microbial biofilms. Disinfect, heat sterilize, or replace shower heads especially if vulnerable populations have access to the showers.
  4. Adjust valves back to normal operating positions to ensure that the system is rebalanced.
  5. Return hot water systems to normal operating temperatures.
  6. Document all start up actions in the daily maintenance log.
  7. Evaluate the effectiveness of your startup procedures relative to Legionella by testing for Legionella using an approved culture method. Collect samples at least 48 hours after final flushing and return of normal operation of the water system. Samples collected too early may give false negative results1. Collect samples from critical locations2 (CDC toolkit). The CDC maintains a list of labs certified for legionella testing. Only use certified labs for testing.
  8. Since there are no Legionella drinking water standards in Florida, you may use the European Union Action levels for Legionella in Potable Hot and Cold Water Systems3 to evaluate test results and identify additional steps needed.


  1. European Society of Clinical Microbiology and Infectious Disease - Guidance for Managing Legionella During the Coronavirus Pandemic 2020
  2. CDC Toolkit: Developing a Water Management Program to Reduce Legionella Growth and Spread in Buildings
  3. European Technical Guidelines for the Prevention, Control and Investigation, of Infections Caused by Legionella species. June 2017