Curbing Legionella Growth Risk in Public Hot Tubs

Three of the main causes for legionella growth are temperature, water age and stagnation. These become huge red flags if hot tubs are not properly maintained. Hot tubs are generally kept at a temperature between 100°-102° as seen in the graph below this is a prime temperature for legionella growth.

Legionella temperature versus growth chart
Note: The above indicators are based on ideal laboratory conditions with new, clean pipes that do not have sediment, biofilm, etc.

Water age is also key due to the dissipation of chemicals in the water. Hot tubs operate at higher temperature. In higher temperatures disinfectants disperse quicker than in lower temperature which makes it critical that we monitor our disinfectant levels continuously. The third is stagnation. When water sits, it is more likely to grow legionella and other pathogens.

Below are some ways to combat these red flag areas when operating a hot tub for public use.

  1. Know what you are doing.
    • There are many resources available for certification and training for operating hot tubs. Make sure that your people are trained on testing and maintaining quality water conditions.
    • Have trained professionals on site during peak use times. Hotels will see peak times of hot tub use on the weekends. Make sure trained staff is on site during this time to maintain water quality.
  2. Test.
    • Maintain your disinfectant levels. Hot tubs should be operated with 3-10 ppm of chlorine or 4-8 ppm of bromine.
    • PH levels should be kept between 7.2-7.8
    • Test for these two twice a day. Preferably hourly during heavy use periods.
    • Log these testing results as well as any additions of chemicals to maintain these levels daily.
  3. Clean Regularly.
    • All systems are different but maintain filtration and recirculation standards to factory specs of your system.
    • Any slime layer is biofilm. These layers are breeding ground for bacteria. Inspect regularly for any slime build up on filters or recirculation systems and clean as needed.
    • Scrub hot tub regularly to clean any slime layers.
    • Drain and replace hot tub water as needed. There are many factors such as number of weekly users and water quality. You want to maintain a clean hot tub and maintain your chlorine and PH levels. Empty and refill as needed.
    • Shock the system with a biocidal treatment on a daily to weekly basis as needed.

Curbing Legionella starts with a well-developed Water Management Plan, which pays for itself through a safer water environment for your facility and a lower potential Legionnaires’ Disease liability for your organization. Take our CDC Legionella Risk Assessment to see where you stand.

Contact Nancrede Engineering to learn more.

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