Property owners must address the Legionella risk – rationality is key in energy savings

10.11.2022 13:45

Reducing energy consumption at home is a hot topic. While it is important to reduce consumption, the impact of reductions on health should be addressed. Legionella bacteria are among those factors to be taken into account, and municipalities will increase related monitoring at the beginning of next year.

Legionella bacteria are the best-known causes of diseases in buildings’ water systems. If Legionella bacteria can reproduce in pipelines or water tanks, aerosols may also carry them into the air. When we then breathe this air, we may catch an infection called legionellosis. The disease can range from a symptomless infection to severe pneumonia.

Legionellosis is an infectious disease to be monitored under the Communicable Diseases Act. Whenever a physician or laboratory discovers a Legionella infection, they must report it to the Finnish National Infectious Diseases Register maintained by the Finnish Institute for Health and Welfare (THL). The aim is to identify sources of Legionella infections to prevent any new cases.

Amended tap water decree: from the monitoring of infections to their prevention

Following the new EU directive on the quality of water intended for human consumption, the amended tap water decree (1352/2015) will enter into force on 1 January 2023, as a result of which municipal health monitoring will pay special attention to Legionella bacteria.

“Until now, the law has only required the monitoring of Legionella infections. In the future, the prevalence of Legionella bacteria in buildings’ water systems will also be monitored based on risks. The problem will, in a way, be approached from two different directions,” says Marjo Niittynen, senior researcher at THL.

In practice, this means that, in pre-defined “primary” facilities, risk assessments must be conducted for water systems. Such facilities include hospitals, public pools and hotels. In risk assessments, information about a building’s water system will be used to assess whether the Legionella risk has increased. If a health inspector finds the risk to be higher than normal, the building owner can be obligated to carry out certain measures, such as monitoring the temperatures of hot and cold water, and monitoring the Legionella situation using samples.

What can property owners do to prevent Legionella bacteria?

Marjo Niittynen, senior researcher at THL, and Jaana Kilponen, senior officer at the National Supervisory Authority for Welfare and Health (Valvira), list ways for property owners and regular people to prevent Legionella bacteria.

“The home is often a source of infections. At home, ensure that hot and cold water temperatures are correct, taps are used regularly and water fixtures are in good condition. These are key measures,” says Niittynen.

This means that after interruptions in water supply, for example, the first litres of water must end up directly in the drain. It is particularly important to ensure that the temperature of hot water is over 55 degrees and that of cold water is under 20 degrees. Hot water is not supplied hot – it is heated in buildings. Each property owner can prevent the spread of Legionella bacteria in their buildings by ensuring a sufficiently high temperature for hot water to prevent any bacteria from growing in pipes.

A question-based tool is being prepared for building owners for use in risk assessments of water systems. Kilponen says that the tool to be published on the Valvira and THL websites at the beginning of 2023 will be available to everyone who needs it.

While it is important to reduce energy consumption at home, the impact of such reductions on health must be considered. For more information, read THL’s tips for cutting down on energy consumption ( and the nationwide “Down a degree” energy saving campaign (

For more information, please contact:

Jaana Kilponen, senior officer, +358 295 209 621