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Legionella Water Treatment

What to Do If You Get a Positive Legionella Test in Your Water System?

Getting a positive Legionella test in your domestic water system is not the kind of news any healthcare facility wants to hear, but there are steps you can take to mitigate the situation and protect the people on your site. In this article, we provide a roadmap to basic steps you can consider immediately upon getting a positive test. Although a positive test is distressing information, the good news is that you’re aware of this early on exactly because you implemented testing for Legionella. Proactive testing is the most important thing you can do to protect the people around you.

For the purposes of this article, we are talking about domestic hot water systems in a building or facility. Although Legionella can be found in cooling towers, the bacteria primarily grow in a domestic hot water system, and that’s where it impacts users such as in a healthcare facility. The bacteria can be detected in hot tubs, ice machines, decorative fountains, spas, and any place water from a system is dispensed or collects.

Positivity Rate

Typically, any distal site positivity rate above 30 percent means that the people in your building could be at risk of contracting Legionnaire’s Disease. For example, if water from ten locations in your building is collected and tested, and more than three of those locations come back positive, that is considered a higher than 30 percent positivity rate.

While a rate lower than 30 percent still requires action, the likelihood of people contracting the bacteria is much lower. Multiple studies have shown that the risk for Legionnaire’s Disease increases significantly with distal positivity rates above 30 percent. If your positivity rate is lower than 30 percent, we recommend calling a consultant like ChemREADY to find out what to do.

Consult Your Water Management Plan

The first step upon getting any positive Legionella hit is to consult your water management plan. If you don’t have a plan, you should consider creating one, and healthcare facilities are required by the Centers for Medicare and Medicaid Services (CMS) and soon, the Joint Commission, to maintain one. Your water management plan should clearly spell out the steps to take when you determine that your water system contains Legionella.

In the following paragraphs, we outline specific action steps you should consider mitigating and ameliorate a positive Legionella test at your facility and protect your users.

Consider Point-of-Use Filters

The first option is installing point-of-use filters at any location in your facility where water exits the system. This could include faucets, shower heads, ice machines and any other point of exit where water is used or consumed by the people who use or live in your building. This means attaching a physical barrier (a filter) between the water system and the point of exit. For faucets and shower heads, for example, maintenance personnel must remove aerators and attach filters. Submicron filters capture all the bacteria and remove it before the water exits. While this does not kill the bacteria in the system, it is an immediate step in remediation because it protects the people using water in your facility.

The disadvantage to point-of-use filters is that it can be costly and time consuming, especially for larger facilities like hospitals. Filters typically last for only 2 to 4 months; therefore, they must be removed and reinstalled at each outlet when they expire. This can be a very extensive, labor-intensive undertaking, yet it is your first point of contact between people and your water system.

Choosing the right filters to install could be confusing, so we recommend contacting ChemREADY to explore pricing options for point-of-use filters.

Shock Disinfection Methods

Another option for remediating a positive Legionella test is shock disinfection, which can be applied using three different methods: thermal heat and flush, hyperchlorination and copper-silver ionization.

Thermal heat and flush

The thermal heat and flush method of shock disinfection requires maintenance personnel dial up the temperature at your hot water source, ideally above 160 degrees Fahrenheit. Then they’ll need to go to each point of use, open each outlet and flush the heated water. You are simply using heat to physically destroy the bacteria within the pipes and then flushing the system.

A thermal heat and flush are easy to perform if your water heating system can achieve the high temperature. It requires no chemicals, tools, special knowledge, or outside help. You simply turn up the heat to the required temperature and immediately flush. At most, a thermal heat and flush requires a phone call to a consultant for advice and recommendations.

Disadvantages to a thermal heat and flush are the risk of people being scalded by the hot water and the time consumption of going to each outlet to flush the hot water. In addition, water pipes may be damaged if they are not designed to operate at higher-than-normal temperatures.

While a thermal heat and flush is easy to perform, there is no guarantee that it will eradicate the bacteria. Over a period, it could temporarily drop the Legionella levels, but that does not guarantee that the biofilm on the pipe walls will be destroyed, and the bacteria could persist. Many bacteria are hardy and may protect themselves, and the Legionella could grow again.


If a thermal heat and flush is not feasible, or if subsequent tests still come back positive, you should consider performing a hyperchlorination. This is the second shock disinfection method.

Hyperchlorination consists of injecting chlorine directly into the potable water system and then opening all the outlets, like heat and flush. You must then verify with full test strips to check whether the chorine levels are adequate to destroy the bacteria and the biofilm inside the pipes.

Again, this method requires a lot of labor. It is time consuming, and it requires that no water can be used from the system until the entire process is completed. All outlets must be flushed, and then the chlorine levels must be checked until they are back to safe levels before people can use the water again.

Hyperchlorination cannot be done by facility staff. It must be performed by a water treatment professional, qualified plumber, or consultant.

Copper-silver ionization

The third shock disinfection method is copper-silver ionization, which is done using special rental equipment that hooks up to the water system. The copper-silver ions interact with and oxidize the bacteria inside the system, destroying the biofilm and bacteria inside the pipes.

Copper-silver ionization is more efficient than thermal heat and flush and hyperchlorination, but it is much more costly, and it may require plumping modifications. You will need outside help and expertise from someone who has the equipment and knows how to operate it.

Supplemental Disinfection

After performing the above remediation steps, if retesting shows reemergence of Legionella, you should consider supplemental disinfection. Supplemental disinfection means adding low doses of disinfectant to the water system to continually destroy any emerging bacteria. This could mean injecting low doses of additional chlorine or other chemicals into the system at levels that remain safe for human consumption.

The EPA has approved three chemicals for water disinfection: chlorine, chlorine dioxide and monochloramine. Monochloramine is becoming more common for used in large city drinking water supplies because it is more effective and has a longer stay time than chlorine.

Secondary disinfection could incur capital improvement costs, so we recommend contacting ChemREADY to explore pricing options for secondary disinfection systems.

In Summary

The only way to know if you have Legionella in your water and to mitigate any Legionella problems is to proactively test for the bacteria. Currently, CMS has a memorandum that require water management plans by healthcare facilities, but it is left up to each facility’s discretion whether and how often to test. We recommend that no matter what kind of facility you operate, you should develop both a water management plan and regular testing schedule to keep your water users safe. Legionella is highly litigated, and it is wise to test regularly and have a water management plan and abide by it. Regular testing gives you the information you need to detect Legionella, act if detected and protect everyone in your facility.

Contact ChemREADY’s consultants to learn more about Legionella testing and remediation programs.

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