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Water Temperatures and Legionella


At the first glance, guidelines may lead engineers and facility operators to conclude that controlling Legionella bacteria in plumbing systems can be accomplished long-term by simply raising water heater temperatures.

As with any solution that appears easy and cheap, it is important to check the fine print.

First, understand that water temperatures are just a small part of a comprehensive Legionella prevention program.

Second, understand the limitations of water temperatures in controlling Legionella. Increasing hot water temperatures may not be an option because of regulations. Mixing valves may help with Legionella control in some systems but not in others. And, reducing cold water temperatures may be infeasible or impractical.

Third, don't assume Legionella control based on temperatures. Even if water can be maintained within the temperature range typically recommended for Legionella control, the results for real plumbing systems will very likely be different than the results for the piping loops set up for the laboratory studies on which the recommended ranges were based.

Water temperature management must be given its proper place within a Legionella prevention program – no more and no less. Target temperatures must be set thoughtfully, achieved safely, and measured. As with the entire Legionella management plan, the effectiveness of water temperatures in controlling Legionella cannot be guaranteed and must therefore be validated rather than assumed.

For more on this topic, click on the article, "The Fine Print" (PM Engineer, October) on the free articles page.

For the important nuts and bolts details about setting and maintaining water temperatures and fixing water temperature problems, register for the online course, "Water Temperatures and Legionella in Plumbing Systems."


  • Haydn Harris Wednesday, 26 February 2014

    In my experience, it is not the use of temperature or indeed any other control measure that presents a problem at all but the implementation of the control/ergo the human factor. Failure to effectively implement any regime will result in failure.

    Validation in this instance does not necessarily mean undertake sampling but validation of the regimen as a whole.

    An interesting article that I hope sparks some debate.

    The link from the HC Info email/newsletter does not work and needs redoing.

  • Matt Freije Wednesday, 26 February 2014

    Haydn: Thanks very much for your input and for telling us about the broken link.

  • Diny Dikken Friday, 25 April 2014

    I've been actively impliyng legionellaprevention programs for over a hundred buildings for almost nine years. We hardly find any bacteria in the hot water, as long as it is over 55 degrees Celsius. We do monitor the temperatures on a regular basis. A weekly assesment of the temperatures keeps the hotwatersystems safe for use. It is a proven method.

  • Matt Freije Friday, 25 April 2014

    Diny: Thanks for sharing your experience. In most US states, regulations prohibit temperatures at 55 Celsius in some types of buildings, to reduce the risk of scalding. But, for those who have the option, it's helpful to know you've found good Legionella control at that temperature.

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More Information

"Deciding Whether to Test for Legionella"

Matt Freije addressed this topic in a webinar presented on June 4th. Click below to view the webinar at no charge.

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