Legionnaires disease and Legionella is a potentially fatal form of pneumonia and was coined in 1977 when a mysterious illness was attributed to bacteria found in a hotels air conditioning system.
Now, duties under the Health and Safety Act mean that Landlords must understand, control and prevent any risks from the bacteria.
Luckily, this does not mean an expensive detailed assessment and a simple report showing there are no real risks is sufficient. However, it is important to reassess should there be any changes in the water system.
You can read the Government guidelines to Legionella on the Health and Safety Executive website. Below are links to a couple of relevant articles that will inform you of your obligations and measures the tenants can put in place to ensure risk is kept to a minimum.