Legionella — hot water temperature and self-monitoring

Legionella bacteria multiply in water between roughly 20 and 45 °C and are suppressed by higher temperatures. That makes hot water temperature the single most important parameter in an apartment building, and it is regulated. Since 1 July 2025 the requirement sits in Boverket's regulations and general recommendations on protection with regard to hygiene, health and the environment, BFS 2024:8, which replaced BBR on this point.

What changed at the same time is less well known and practically important: the 60 °C rule is no longer in the building regulations.

What the regulation requires

BFS 2024:8 Chapter 8, Section 6 states that tap water installations must be designed so that microbial growth is not promoted, and further:

• Hot tap water installations must be designed so that a water temperature of at least 50 °C can be reached at the tap.
• Circulation pipes for hot tap water must be designed so that the temperature does not fall below 50 °C in any part of the installation.

The materials used must also be such that they do not promote microbial growth.

Where the 60 °C rule went

The recommendation that stagnant water in cylinders and accumulators should not fall below 60 °C has long been cited as a building requirement. It never was one — it stood as a general recommendation to the old BBR 6:621.

BFS 2024:8 contains no general recommendations at all. When BBR was replaced, the recommendation did not carry over, and the 60 °C level survives today in the Public Health Agency's guidance on self-monitoring of water systems, where it is recommended as part of the property owner's self-monitoring.

The conclusion for a portfolio is undramatic but should be drawn deliberately: do not lower cylinder temperature because the recommendation left the building regulations. The level is based on how the bacterium behaves, not on where it happened to be published, and it remains the recommended starting point for self-monitoring.

Building rules apply to building — self-monitoring applies always

This is the distinction that determines what actually governs your existing buildings. BFS 2024:8 is a building regulation: it governs how an installation must be designed when it is erected or altered. It imposes no ongoing operational requirements on a completed building.

For the existing building the duty comes instead from the Environmental Code: dwellings must be used so that no detriment to human health arises (Ch. 9 s. 9), and you must continuously plan and check operations to prevent it (Ch. 26 s. 19). See self-monitoring under the Environmental Code.

In practice: the temperatures above are design requirements at construction and checkpoints in self-monitoring during operation.

The risk points in a residential portfolio

• Long dead legs from the circulation loop to individual taps. Water in the dead leg does not circulate and cools.
• Unused flats and premises. Stagnant water is the classic growth condition, and empty flats between tenancies are the most common instance.
• Circulation loops that have drifted out of balance. A loop can sit below 50 °C for years without anyone noticing, because the complaint is "it takes a while to get hot" rather than "we have a legionella problem".
• Mixers and shower hoses left unused, for example in laundry rooms and communal areas.
• Energy-saving measures where the flow temperature has been lowered without checking the temperature at the tap.

Can we lower the hot water to save energy?

Not below 50 °C at the tap. That is where the legionella risk begins, and it is also the level the building rules design against. The energy saving lies instead in reducing distribution losses — insulating circulation pipes, rebalancing, shortening dead legs — not in lowering the water temperature.

It is worth stating explicitly because the proposal recurs, often with reference to recommendations in the energy certificate. A recommendation that would take hot tap water below 50 °C at the tap should not be implemented.

What self-monitoring should contain

1. Fixed measuring points — the cylinder or accumulator, the return of each circulation loop, and a number of taps at the far end of the system.
2. Interval and log. A reading without a date and a location cannot be compared over time, and it is the trend that shows a loop drifting out of balance.
3. A routine for unused spaces — flushing taps in empty flats and premises. The Public Health Agency's guidance specifically notes that buildings, or parts of buildings, that are periodically unused need expanded self-monitoring.
4. A response routine for low readings or suspected legionella, naming who is contacted.

Points one and three are the ones that have effect. Point three is also the one that is forgotten, because an empty flat has nobody to complain.

In Emphyx, temperature checks can be added as items in the inspection round checklists alongside the rest of self-monitoring, so readings land on the right building with a date. We measure nothing ourselves, analyse no water samples and make no legionella risk assessment — that is a plumbing question, and on confirmed infection a matter for the environmental committee and communicable disease control.