Design temperatures and the Legionella band

Keeping cold water cold

Legionella can multiply in water roughly between 20°C and 45°C when nutrients and other suitable conditions are present. This range does not mean growth is equally fast throughout it. The control aim for cold water is to keep it below 20°C wherever practical, so it stays out of that band. Below about 20°C the bacteria are generally dormant. Thermal disinfection needs sufficient temperature and exposure time; neither a cold reading nor a brief hot reading proves sterilisation.