Guideline for the assessment of water quality risks in buildings’ water systems – to prevent the spread of Legionella bacteria

17.2.2023 08:46

Based on the Health Protection Act (763/1994) and the Decree on Domestic Water (1352/2015), which were amended on 12 January 2023, special attention will be paid to Legionella bacteria. The purpose is to prevent health hazards caused by buildings’ water systems through risk assessments and, if necessary, monitoring.

Legionella can cause a severe pulmonary infection called legionellosis. An average of 30 cases are recorded in Finland per year. The most common infection route is the inhalation of water aerosols in the shower or a hot tub. Legionella bacteria are not transmitted through drinking water.

Prevention of Legionella bacteria

To prevent Legionella bacteria, property owners are advised to carry out a water quality risk assessment of their buildings’ water systems. Risk assessments are a regulatory requirement for buildings where a large number of people may be exposed to water-related risks. Examples of such buildings include accommodation facilities, public spas, public indoor and outdoor pools and saunas, social welfare units providing enhanced assisted living services or institutional care, and hospital and public healthcare centre wards.

It is particularly important to ensure that the temperature of hot water is over 55 degrees and that of cold household water is under 20 degrees. A sufficiently high household water temperature prevents Legionella bacteria from growing in water systems. Hot water is not supplied hot – it is heated in buildings.

Guideline for water system risk assessments

A guideline for the assessment and prevention of water quality risks associated with Legionella bacteria and lead ( (in Finnish) has been published for building owners in Finnish. The guideline and its appendices are available to everyone who needs them. The problems caused by Legionella bacteria may be more common than expected, but lead is not generally a problem in Finland, unlike in many countries in Central Europe.

- “The guidelines and the related forms have been prepared for building owners in particular, so that they can assess and manage health risks in buildings’ water systems, especially in terms of Legionella bacteria,” says Jaana Kilponen, senior officer at the National Supervisory Authority for Welfare and Health (Valvira).

The guideline provides information about the risk assessment and risk management of buildings’ water systems, as well as the risks caused by Legionella bacteria and the prevention of risks. It also covers measures that can be taken if a building’s water system contains more Legionella bacteria or a higher concentration of lead than the threshold limit allows, or when health hazards are believed to exist. The appendices to the guideline include a form for water temperature measurements in water systems (Appendix 1) ( (in Finnish) and a checklist for risk assessments of buildings’ water systems (Appendix 2) ( (in Finnish).

The checklist in Appendix 2 is a good risk assessment tool. Kilponen encourages people to use the risk assessment checklist, answer the questions honestly and consider possible corrective measures.

- “Temperature measurements are an essential part of risk assessments, and much can be achieved if the owner of the building ensures that measurements are made at a sufficiently large number of water supply points. This provides information about any risk of Legionella bacteria in the building,” says Kilponen.

Further information: Jaana Kilponen, senior officer, tel. +358 295 209 621, tesu(at)