How Temperature Influences Legionella Growth

How temperature influences legionella growth

In this review the experts at Legionella Control International look at how water temperatures influence legionella growth and how this information can be used to control the risks from the bacteria.

Under certain circumstances Legionella bacteria can lead to serious illness and fatalities in humans. Since Legionella bacteria can exist in man-made water systems, it is imperative to ensure the water is stored, maintained and distributed at temperatures that do not encourage the growth and spread of the bacteria.

There are three temperature ranges that have an influence on the growth and proliferation of Legionella bacteria. We’ll look at each of these below.

Can legionella grow in cold water?

Contrary to what some may believe, Legionella bacteria do not die off as water temperatures drop below 20 degrees Celsius. Instead, they become inactive and unlikely to cause harm. It’s also important to remember that they do not multiply while in this state.

However, if water at this temperature is released for use and it is warmed during that process, it may lead to some potential for Legionella bacteria to cause harm. A risk assessment should consider whether that is the case.

What happens to legionella at temperatures of between 20 and 45 degrees Celsius?

Water temperatures between 20 and 45 degrees Celsius provide the ideal range to allow the bacteria to grow and multiply. If Legionella are permitted to remain in water at this temperature, the whole water system concerned is at risk of infection, and this can occur very quickly. This puts anyone who uses the water system at potential risk from Legionnaires’ disease.

How do you kill legionella?

Once hot water temperatures reach 50 degrees, the Legionella bacteria will begin to die off. The speed at which this occurs depends on how high the temperature goes, the hotter the temperature the more effective the kill rate.

A two-hour period where the water is maintained at 50 degrees Celsius will get rid of 90% of the bacteria. If the temperature of the water is raised to 60 degrees Celsius, the same percentage of bacteria will die in just two minutes. Raise that temperature again to hit 70 degrees Celsius and all the Legionella bacteria present will die straightaway.

What are the official guidelines on water temperatures?

In the UK all water should be kept above or below the optimum range mentioned above.

Hot water supplies should be stored at a minimum of 60 degrees Celsius.

Typically, any hot water that comes back into the heating system should achieve a minimum temperature of 50 degrees Celsius to keep it above the risk zone. In hospitals and healthcare environments the water return temperatures should be at least 55 degrees Celsius.

Similarly, cold water supplies should never go above 20 degrees Celsius. Again, the idea is to ensure all supplies remain outside the danger zone.

What is thermal disinfection?

Thermal disinfection involves keeping the cold water below 20, and the hot water hot at a minimum of 50 degrees Celsius (55 degrees Celsius in healthcare). If this is achieved, the risk of Legionella bacteria having the opportunity to grow and spread in a water system will be significantly reduced.

International legionella and water safety specialists

Our teams of water safety specialists support those responsible for the control of waterborne pathogens including Legionella bacteria in the workplace, helping them to protect their people and meet their health and safety obligations in this specialist area. We deliver professional water safety legionella risk assessments, water testing, independent compliance auditing, City & Guilds training and other environmental risk management services that help keep staff and others safe.

If you have questions about any of the issues raised above or you would like to speak with one of our legionella specialists please call us today on 0330 223 36 87 or contact us here.