With the right environmental conditions, any water system could be a source for Legionella growth. As an employer or manager of premises, it is your responsibility to understand your water systems and be aware of the areas which are likely to create a risk from exposure to Legionella in order to maintain all the right checks.

These are some of the key areas to look out for in your water systems that could encourage Legionella growth:

Hot and cold water systems

Hot and cold water systems are a crucial area of maintenance when it comes to Legionella risk. Certain areas within hot and cold water systems create conditions which are suitable for colonisation and multiplication of bacteria, such as water that is stored between 20-45°C. To avoid this risk, cold water systems should be maintained at a temperature below 20°C. Additionally, hot water should be stored at least at 60°C and distributed at a temperature of around 50°C.

Thermostatic mixing valves (TMV), a device that controls water temperature for baths, showers and other outlets by mixing hot and cold water to produce a temperature controlled flow of water, are another area within hot and cold water systems which can present risk of Legionella growth. TMVs must be regularly stripped down for cleaning, descaling and disinfecting in order to ensure there are no bacteria within the valve.

Within any water system the presence of dead legs and dead ends (capped pipes) should also be regularly checked to maintain Legionella risk. These areas, especially where optimum temperatures are present, can encourage microbial growth and stagnation to occur. This risk is also significant in infrequently or unused outlets, such as a showers, and areas of the system where circulation is inadequate.

Other Legionella growth areas of risk

There are a number of other areas within any water system which can present similar high risk conditions for the growth of Legionella. For instance any system in which water is recirculated including spa pools, hot tubs, whirlpool baths and other spa facilities as water is not discharged after use. Other areas of risk include systems which are susceptible to thermal gain when operating, making it difficult to maintain the required safe water temperatures to prevent bacterial growth. This is largely true of any water systems which operate outdoors. Fountains, decorative water features and irrigation systems are at risk of using water that falls within the temperature risk zone due to influence from the external environment. All of these systems also have the added risk of the capacity to generate aerosols and should therefore undergo regular Legionella checks in order to maintain safe and healthy conditions.

For an overview of the conditions which encourage Legionella growth, click on the infographic below: