Organisations, or self-employed individuals, who provide residential accommodation or who are responsible for the water system(s) in their premises, are responsible for ensuring that the risk of exposure to legionella in those premises is properly controlled. This means that they have a duty to assess the risk from exposure to legionella to their staff, residents, guests, tenants and customers by implementing appropriate control measures. This is especially important in residential buildings, where vulnerable people may be at risk, such as retirement flats, or where the accommodation is provided specifically for a group who may be susceptible to legionelloses.