CLAGE
15
Recommendations based on European standard CEN/TR 16355
Legionella are rod shaped bacteria which are a natural constituent of all fresh waters.
Legionaries’ disease is a serious pneumonia infection caused by inhaling the bacteria Legionella pneumophilia or
other Legionella species. This bacterium can be found in domestic, hotel and other water systems and in water used
for air conditioning or air cooling system. Hence the main intervention against the condition is prevention, through
control of the organism in water systems.
The European standard CEN/TR 16355 gives recommendations for good practice concerning the prevention of
Legionella growth in drinking water installations but existing national regulations remain in force.
General recommendations
“Conditions for Legionella growth”. The following conditions encourage Legionella growth:
• Water temperature between 25 °C and 50 °C. To restrict the growth of Legionella bacteria, the water temperature
shall be in a range that the bacteria will not grow or have minimum growth, wherever possible. Otherwise, it is
necessary to disinfect a drinking water installation by means of a thermal treatment;
• Stagnation of the water. To avoid long periods of stagnation, the water in every part of the drinking water installa-
tion should be used or flushed at least weekly;
• Nutrients, biofilm and sediment within the installation including water heaters, etc. Sediment can support the
growth of Legionella bacteria and it should be removed on a regular basis from e.g. storage systems, water heat-
ers, non-flown through expansion vessels (e.g. once a year).
Regarding to this storage water heater, if...
1. the product is switched-off for a period of time [months] or
2. the water temperature is permanently maintained between 25 °C and 50 °C,
the Legionella bacteria could growth inside the tank. In the second case, the anti-legionella function starts automati-
cally.
Anti-legionella function
If the water does not reach 65 °C in 14 days, the anti-legionella function switches on and the water in the appliance is
heated to 70 °C; this temperature is maintained for 120 minutes.
2. Legionella prevention
Basically Legionella can come up again when the water temperature drops below 55 °C.
