Legionella prevention in practice

Maintain at least 60 °C in the hot-water cylinder (storage), at least 50 °C at the furthest draw-off point within 10–20 seconds of opening and at least 50 °C in the circulation return — nowhere below 50 °C in the hot-water circuit. The risk zone for legionella growth is 20–45 °C.

Set up circulation in the hot water system so the temperature is maintained all the way out to the furthest outlets — not just down in the cylinder. Without circulation, the water cools in the pipes and ends up in the risk zone.

Avoid unnecessary dead legs and oversized pipe dimensions that lead to stagnant water. Rarely used draw-off points and long dead-end branches are classic growth sites, because the water stands still and cools down.

Insulate cold- and hot-water pipes separately, so that the cold water is not unintentionally heated into the risk zone and the hot water does not lose temperature. The separation protects both circuits.

Energy considerations push towards approx. 55 °C in the cylinder to save heat loss and limescale, but the standard requires 60 °C. Lowering it increases the Legionella risk, especially in large circulation systems — follow the standard and keep 60 °C in the cylinder.

The standard beats energy saving: keep the cylinder at 60 °C.

Document temperature measurements at the cylinder, the furthest draw-off point and the circulation return in a Legionella log with date, result and signature. The log is part of the QA documentation and proves that the requirements are met over time.

Extended domestic water systems should have a bacteriological check at least once a year. From 1 January 2025 «priority properties» (hospitals, care homes etc.) have mandatory sampling and reporting to the municipality — check whether the property is covered.