Preventing the growth and health risks of Legionella

This page provides guidance on how the different parties involved can contribute to preventing the growth of legionellae in water systems, reducing the risk of illness, and preventing new cases.

The prevention of Legionella infections, the measures taken to combat them and their monitoring are also guided through legislation. Under the Health Protection Act, the risk assessment obligation concerning water systems, which entered into effect on 12 January 2023, concerns hospitals, swimming pools and hotels, for example. 
Legislation and guidelines relating to legionellae

On a sub-page, we explain how to prevent the risk of Legionella when it is necessary to temporarily interrupt the use of the water system for a shorter or longer in exceptional circumstances:
Combating the risk of Legionella during an interruption in the use of water systems

Resident or property owner

How to prevent Legionella in your home:

  • Check the domestic hot water temperature. In new properties built or renovated after 2007, the temperature of hot domestic water must be at least 55 °C and in old properties built before 2007, at least 50 °C throughout the water system.
  • If you do not obtain water of between 50 °C and 55 °C from the taps within a reasonable waiting period, notify the property manager or adjust the temperature of the hot water yourself so that it is at a sufficient temperature. Occasionally run the hottest possible water (at least 50–55 °C) from the taps and shower for about 1–2 minutes.
  • Check the cold water temperature. It should be below 20 °C.
  • Use all water points on a regular basis, preferably daily.
  • After breaks in water use, run the first litres of water directly into the drain.
  • Drain the water from a domestic whirlpool after each use. Learn how to clean the whirlpool and its plumbing.
  • Take care of swimming pool water chlorination and other cleaning.

Housing manager and maintenance personnel

  • Make sure that the temperature of domestic hot water for all water points is at least 50–55 °C. The temperature of the returning water should also be at least 50–55 °C, which means that the temperature of the outgoing hot water must be significantly higher. The temperature of hot water in newer water systems, meaning water systems built or repaired after 2007, must be at least 55 °C. It is wise to try to have this temperature in older properties as well in order to prevent legionellosis cases.
  • Make sure that cold water is cold, below 20 °C.
  • If your property has an open cooling system with a cooling tower, make sure it is serviced, disinfected and safe. Find out if legionellae are present and ensure that prevention measures are taken regularly.
  • If your property has a humidifier, make sure that the humidifier is serviced and disinfected regularly.

Hotel Safety Officer

More information:

Health inspector or environmental inspector

  • Act as a support for residents and property managers, especially in obtaining hot enough water for all residents.
  • Require the property owner to take measures to eliminate health hazards upon the discovery of any Legionella-related deficiencies.

Occupational Safety Officer

The risk of Legionella is different at different workplaces and depends on the water system, its use and risks. Instructions for Legionella prevention suitable for usual water use purposes are available in the above instructions for residents and housing managers.

A high-risk workplace:

Legionellae may be present in high concentrations, for example, in various cooling waters, industrial process waters and wastewater treatment plants.

  • Obtain information about Legionella bacteria and carry out a risk analysis of the water systems in the workplace to identify the risks associated with legionellae. If necessary, have Legionella analyses conducted.
  • Make sure that the growth of Legionella bacteria in water systems is prevented. 
  • Be aware that at wastewater treatment plants,  exceptionally high Legionella concentrations can be detected, especially when  hot industrial wastewaters are cleaned.
  • In some dirty water systems that contain large amounts of legionellae, such as waste water systems, it is difficult to control Legionella. In that case, the risk of Legionella can be reduced, for example, by wearing personal protective equipment.
  • Also see to the safe processing and further use of sewage sludge.

HVAC and plumbing system designer

  • Pay attention to the cooling of water during the hot water cycle: Two short hot water cycles are a more effective solution for fighting legionellae than one long one.
  • Place water points only in locations where there will be regular daily use.
  • Place the cooling tower exhaust air outlet as far as possible from the ventilation inlet and from people moving around close to the property.
  • Find out about the possibilities of using sealed cooling solutions and district cooling at the locations being designed.
  • Design the properties so that all the inlet waterlines receive regular use.


  • Be aware that, in addition to the risks faced while abroad, people can also be exposed to Legionella in Finland, for example, at home, at work or at a hospital, spa, swimming pool or hotel.
  • Pay attention to the possibility of legionellosis in cases of pneumonia. It is likely that legionellosis cases are still underdiagnosed in Finland.
  • In cases of suspected legionellosis, find out also if there could be several cases involved.
  • Report Legionella infections to the National Infectious Diseases Register. This information is used to identify any connected cases and to prevent new cases emerging.

On our website

Microbiological water analysis
Analysing water samples and determining sources of infection

Laboratory studies of Legionella (in Finnish)
Clinical samples and typing of legionella strains (on the Infectious Diseases and Vaccinations website)

Legionella (in Finnish)
Information on transmission, detection, symptoms and treatment (on the Infectious Diseases and Vaccinations website)

Elsewhere on the web

Drinking Water Directive (EUR-Lex)
Directive (EU) 2020/2184 of the European Parliament and the Council on the quality of water intended for human consumption

ESGLI: Legionella infections
Website of the ESCMID Study Group for Legionella Infections (ESGLI)