Legionella are bacteria, commonly found in natural water sources such as rivers and ponds, but they can also be found in artificial water systems such as wet cooling towers and hot water systems.
They can cause Legionnaires' disease - a pneumonia-like illness. This is the most well-known and serious form of a group of diseases collectively known as legionellosis. There have been several large outbreaks of Legionnaires' disease involving staff, patients or the general public.
Control of legionella in cooling towers and in hot and cold water systems is required under the HSWA and COSHH. Advice on duties can be found in the ACOP and guidance "Legionnaires Disease: The control of legionella bacteria in water systems. Approved code of practice and guidance. L8, Health and Safety Executive, 2000. ISBN 0 7176 1772 6". Also available are:
There are separate regulations, which require the notification of cooling towers to the Local Authority. These are intended to help identify possible sources of infection during outbreak investigations.