Legionella, the more common term for legionella pneumophilia, is a pathogenic bacterium that is most commonly found in water. Where nutrients are available, legionella will multiply between the temperatures of 20c and 42c. Below 20c legionella will still exist but in a dormant state. Above temperatures of 60c the bacteria will not be able to survive.

The infection caused by legionella is known as legionellosis and can cause serious illness as well as milder symptoms. Legionnaires Disease is a potentially fatal disease and can be contracted from inhaling the mist or spray from a contaminated water source. Milder complaints include Pontiac Fever and Lochgoilhead Fever which display flu like symptoms.

Legionella is naturally occurring in nature and would be expected to be present in water sources such as rivers and waterways. It is when the water source is heated to a higher temperature and there are nutrients it can use to multiply that the legionella becomes a significant health risk.

The water source is not always an external one, but more likely to be found in heated water systems in homes, industrial plants, offices, schools, local authority buildings, pubs, hotels, spas, swimming pools and leisure centres. The bacterium can multiply in any heated water system and this is why there is a legal obligation for the owners of any building with a public water supply to test for legionella and ensure regular management.