Legionella thrives in lukewarm, stagnant water between 20 and 45 °C. The standard keeps the bacterium down with specific temperature requirements: at least 60 °C in the tank, at least 50 °C at the most distant outlet and in the circulation return. Here are the figures and the real conflict with energy savings.
Introduction
Legionella is a bacterium that can cause serious pneumonia if inhaled as misted droplets — e.g. in the shower. It grows in warm tap water that is not hot enough, and in pipes where the water is stagnant. Control is about temperature and circulation.
Temperature requirements
| Location | Requirements (standard) |
|---|---|
| Hot water cylinder / heat exchanger (storage) | ≥ 60 °C |
| Most distant tap point (within 10–20 sec.) | ≥ 50 °C |
| Circulation return to tank | ≥ 50 °C (ingen steder under 50 °C) |
| Risk zone for legionella growth | 20–45 °C |
The requirements have been verified against SSI and industry sources and follow DS 439:2024 + BR18 §§ 403–419. The point is that the water must reach at least 50 °C at the most distant tap within 10–20 seconds — not just be hot down in the tank. (Source: SSI — Legionella in hot water; STPS; FSTA NIR 2025.)
Inspection and prioritized properties
- 01Extended domestic water systems: microbiological control (total + legionella) at least 1 time per year.
- 02From 1.1.2025 'priority properties' (hospitals care homes etc.) have mandatory sampling and reporting to the municipality.
- 03There are no national limit values for bacterial content in hot tap water in Denmark.
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