Why do we ususally heat hot water tanks to 65 degrees?

We do this to prevent Legionella infestations. Legionella is a bacterium that is always available in any source of water. The bacteria spread through small droplets which can be ingested by people nearby the water, for instance when taking a shower. Consequently, they can contract Legionnaires’ disease or Pontiac fever. Compared to COVID-19 for instance, the mortality rate for Legionnaires’ disease is way higher. 10 % of healthy people die and the rate increases for elderly and people with underlying diseases. 

How do we prevent the bacteria from growing? 

There are numerous conditions which increase the risk of Legionella bacteria in a water system. Firstly, the bacterium enjoys temperatures between 20 and 45 degrees. The standard recommendation in the UK is to maintain hot water temperature in pipes and tanks above 55 degrees. Additionally, the presence of biomass and stagnating water provides a suitable environment for the bacteria. 

Most ships today only use temperature control to prevent Legionella growth. This requires a large amount of energy, especially if the water is pumped in a closed loop in order to reduce water consumption. A study by E. Cloutman-Green et al. (2019) showed that lowering the water temperature from 65 to 45 degrees resulted in a reduction of over 33 % in annual energy use. 

But surely lowering the temperature increases the risk of Legionella?

E. Cloutman-Green et al. concluded that a proper water disinfection system does not need temperature control. In their study, there was not found any Legionella bacteria in the system that dosed biocides into the water at temperatures below 55 degrees. The biocides eliminate the biomass, which the bacteria need in order to grow. We provide this system for ships with automatic surveillance which ensures safe potable water on board. As a result, the cold water can be used for drinking water and there is no longer a need for water bottles. Read more about our service or contact us for more information. 

Reference:

- E. Cloutman-Green et al.: Controlling Legionella pneumophila in water systems at reduced hot water temperatures with copper and silver ionization. (2019)