Legionella, scalding and backflow: protecting people

Säker Vatten protects people as well as buildings — from the bacteria that grow in lukewarm water, from scalding, and from contaminated water flowing back into the drinking supply.

Legionella: keep cold cold, hot hot

Cold and warm pipes must not touch, so heat doesn't transfer. Cold-water pipework in shafts and joists is designed so standing cold water stays at or below 24 °C even after 8 hours. There must be no dead-leg branch-offs where water stagnates; future connections are capped or valved to stand empty. A central shower mixer's pipe to the outlets must not exceed 5 metres. After a pressure test the system is put into use within seven days or fully emptied, to stop bacterial growth.

Scalding: cap the temperature at the tap

Hot water leaving the heater should not exceed 60 °C. Where there is special accident risk — pre-schools, for example — mixed water at the tap must not exceed 38 °C. Showers used by people who can't regulate temperature themselves, or fixed showers that can't be adjusted without someone in the shower, need a temperature limiter set to a maximum of 38 °C that can't be changed without deliberate manipulation.

Backflow: protect the drinking water

Backflow protection follows the industry interpretation of the EN 1717 standard. Typical requirements: an air gap of at least 20 mm at open tap outlets; an integrated air gap for WCs, dishwashers and washing machines; check valves — often combined with vacuum valves — for hand-showers and hose connections that could dip below a water surface; and an air gap of at least 100 mm for heating or cooling systems containing additives. The aim is that no used or contaminated water can ever siphon back into the clean supply.

Verified by temperature control

These protections are confirmed by documented temperature checks: at least 60 °C in heaters and accumulators (with a weekly heat-up where heat pumps run cooler), 55–60 °C on hot-water output, at least 50 °C in hot-water-circulation return and circuits, and at most 38 °C at special-risk outlets.

Official source: this is M5's plain-language summary, not the official text. For the full rules see Säker Vatten (sakervatten.se).