In order to counteract the spread of Legionella in principle, u.a. in DVGW worksheet W551 “Technical Measures to Reduce Legionella Growth”.
Since Legionella occur predominantly at a water temperature of 25 ° C to 50 ° C, the worksheet for hot water production plants prescribes a constant flow temperature of at least 60 ° C.
In addition, the return temperature in warm water circulations must not fall below 55 ° C, whereby the difference between supply and return must not exceed 5 ° C. In addition, the worksheet provides weekly thermal disinfection. Here u.a. The entire hot water installation, including all fittings, is heated to more than 71 ° C for at least three minutes and then cooled again with fresh cold water.
In addition to thermal disinfection, other techniques such as ultraviolet light irradiation, nano / ultrafiltration, chemical disinfection and the electrolytic production of sodium hypochlorite have been developed over time.