The cooling system may consist of a cooling tower, evaporative condenser or other cooling element, the re-circulating pipe work, the heat exchanger, pumps and ancillary items such as supply tanks and pre-treatment equipment.
Hot and cold water systems
There are various systems available to supply hot and cold water services that range in size, scale and complexity. All can present foreseeable risk of exposure to legionella. Temperature control is the traditional strategy for reducing the risk of legionella in hot and cold water systems. Cold water systems should be maintained, where possible, at a temperature below 20°C. Hot water should be stored at least at 60°C and distributed so that it reaches a temperature of 50°C (55°C in healthcare premises) within one minute at the outlets.
Spa pools
Spa-pool systems are increasingly popular and can be found in a variety of sizes and settings. They are known by various names including hot spas, hot tubs, whirlpool spas and portable spas. Such systems pose a reasonably foreseeable risk as they are a recognised source of diseases caused by infectious agents including the organism that causes legionnaires’ disease, primarily Legionella pneumophila. There have been a number of outbreaks linked to spa-pool systems in leisure centres, hotels, holiday homes, on cruise ships and on display.
Other risk systems
In addition to evaporative cooling systems, hot and cold water systems and spa pools, there are a number of other risk systems, e.g. humidifiers, air washers, emergency showers, eye wash sprays, indoor ornamental fountains, aqueous tunnel washers etc that could potentially be a source for legionella bacteria growth.
Any water system is potentially a reasonably foreseeable legionella risk if it has any of these factors:
The presence of legionella bacteria in the system water
where the water temperature may be between 20-45 °C,
a means of creating and/or spreading breathable droplets, (aerosols)
stores and/or re-circulates water
likely to contain a source of food for the organism, such as contaminants from the surroundings or process including presence of sludge, rust, scale, organic matter or bioflms
