At what temperature must hot water heaters be set to prevent growth of Legionella bacteria?

Setting hot water heaters to a temperature of 140°F is recognized as an effective measure to prevent the growth of Legionella bacteria, which can cause Legionnaires' disease, a serious form of pneumonia. This temperature is hot enough to inhibit the proliferation of the bacteria, which thrives in environments at lower temperatures, typically between 77°F and 113°F.

Maintaining water at 140°F not only limits the bacteria's ability to multiply but also helps reduce the risk of bacterial contamination in plumbing systems. It is important to note that while higher temperatures, such as 160°F or 180°F, can further deter bacterial growth, they may introduce safety risks, such as scalding injuries, especially for vulnerable populations. Conversely, setting the temperature at 120°F might not provide adequate protection against Legionella, as it could allow the bacteria to survive and multiply.

By keeping the hot water heater set to 140°F, a balance is struck between effectively controlling Legionella growth while also managing safety considerations regarding hot water use.