The Dilemma: Legionella Control vs. Scalding Risk

One of the major concerns we have experienced when writing Water Management Plans for hospitals and Long Term Care (LTC) facilities has to do with temperature setting requirements. Since Water Management Plans for controlling bacteria, such as Legionella, are required in LTC and hospital settings, one important aspect is controlling hot water temperatures. Legionella thrives within a narrow water temperate range of 68°- 122°F. Water Management Plan guidelines developed by governmental agencies recommend setting a hot water tank temperature at >140°F to kill potentially harmful bacteria. Unfortunately, shower or faucet water at 140° can cause a first-degree burn in just 3 seconds.

According to the American Hospital Association, more than 112,000 individuals are admitted into hospital emergency rooms each year for scald-related injuries. The cause varies from unattended bathing care of the elderly, plumbing that is lacking temperature control devices, and bathing of patients with delicate healing tissue concerns.

Facilities that do not have temperature control devices on all fixtures must make an important decision: How can we control bacteria such as Legionella in our water system while making sure our building occupants do not get burned?

Legionella is a type of pneumonia caused by Legionella, a bacterium found primarily in warm water environments. The disease can be contracted by inhaling airborne water droplets containing the bacterium. To control the disease potential, facilities need to control the temperature of the water in their storage and delivery systems. OSHA recommends that domestic hot water should be stored at a minimum of 140°F and delivered at a minimum of 122°F at all outlets to minimize the growth of Legionella. CDC and ASHRAE recommend hot water circulation at a minimum of 124°F and installing temperature control valves at the point of use to reduce scalding risk.


Where do you set hot water heaters and water delivery system piping to reduce the risk of both scalding and legionella exposure? Facilities without temperature control valves should set the hot water temperature to no less than 123°F.  Above 122°F Legionella can survive but do not multiply. At 131°F Legionella die within 5-6 hours. The water temperature delivered to “use” points in the facility should be sampled to make sure the temperature is within the State requirements (usually 115°-120°F) for the prevention of scalding. It is important to flush tanks, check showers and faucets as directed in your facility’s water management program.