Cooling and potable water systems in buildings are well documented as potential sources of Legionnaires’ disease, especially if the prevailing water temperature is between 35-46°C. These systems are an integral part of most large buildings such as office complexes, hotels and hospitals and provide an ideal habitat for legionella bacteria which causes the disease.

Once municipal water leaves a treatment plant, it often travels many kilometres before reaching the user, and during this time the chlorine disinfection residuals can diminish considerably. Because of this building managers often ensure additional disinfection is provided at or near the point of use.

There are several ways of controlling legionella in a building's water distribution system which include maintaining correct water temperatures, copper-silver ionisation and chlorine dioxide. However, a method becoming increasingly popular is ultraviolet (UV) disinfection as UV has many advantages:

• Kills bacteria such as legionella and pseudomonas permanently, without the use of chemicals.
• A clean process, producing no unwanted by-products.
• Systems are small and easy to install within existing pipework with minimal disruption.
• Maintenance is simple and can be carried out by on-site staff with minimal training.

UV systems can be used for virtually all building services applications where legionella is a potential threat. These include:

• Mains water recharge pipes. As mains water can contain legionella, it is important to ensure that water use for charging (or filling) pipes in new buildings is disinfected.
• Stored water. Large public buildings often pump water to tanks located on roofs which are gravity fed to all floors. UV-treating water when it leaves the tank ensures it is free of infection – not just of legionella but all potentially pathogenic micro-organisms.
• Evaporative water coolers. These devices have also been shown to be a potential source for legionella bacteria to proliferate, and treating this water should always be a priority.
• Drinking water and food preparation taps. Unless they are connected to the rising mains drinking water supply, these outlets normally require a UV system for each tap to ensure potable quality is maintained.
• Showers, spas, fountains and other water features. These are well documented as potentially high risk devices due to their increased aerosol production, and as such secondary water treatments should always be considered; particularly in hospitals and retirement homes where occupants may have suppressed immune systems and are more vulnerable to legionella infections.
• Air conditioning. Although ducted air is responsible for many illnesses collectively known as 'Sick Building Syndrome' it may also be responsible for nosocomial infections in hospitals, which are spread by airborne transmission. If there is a source of legionella in other parts of a building, for instance contaminated showers, legionella can carry in aerosol form throughout the entire building via the air conditioning system. Installing UV air treatment systems in air ducts has been shown to reduce airborne bacteria and viruses by over 90%.

UV installations are used worldwide and are increasing in popularity due to their low maintenance and cost-effectiveness in a wide range of water and air treatment applications.

Article by
Hanovia Ltd
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