Legionella in cold water systems

When designing cold water systems water temperature, retention time, pipe material and regular system maintenance is of great importance in order to prevent micro bacterial growth.

Not only hot water systems are at risk of getting infected with microbacteria.

Especially in large and tall buildings cold water often heats up to a level where a wide selection of bacteria can breed. Where the water main enters the building the cold water has a temperature of 8-15 °C. After that point the water temperature starts to increase.

Depending on the consumption the water temperature often reaches the almost same temperature as the surrounding air. The consumer will not only never experience what cold water is like, but the cold water is likely to contain bacteria.

Like other microorganisms legionellae live and feed in biofilm which is found inside pipes and tanks.

Many cold water systems are at risk getting infected but there is an increased risk of growth in systems where:

•         Pipe- and tank insulation is missing or in poor condition. All cold water pipes and tanks to avoid heating

•         Cold and hot water pipes are co- insulated.   

•         There are dead-legs where there is no water flow

•         Roof top tanks and break tanks are used. Tanks should be located inside the building and should be sized with low retention time.      

•         Water tank in organic material. The tank itself will serve as food source for bacteria.    

•         Pipes are oversized. Stagnant water increases risk of bacteria growth.

•         Pipe material can rust. Rust is a good food source for bacteria.

 Cold water systems in buildings with a risk of scaling during low consumption periods should be provided with effective water disinfection system. Such systems should be able to remove both biofilm and kill free bacteria and other microorganisms without affecting taste and smell of the water.

 National building codes, legislation and other national guidelines concerning water systems have to be observed as well.