What is Legionella?
Legionnaires' disease is a potentially fatal form of pneumonia caused by the inhalation of small droplets of contaminated water containing Legionella. All man-made hot and cold-water systems are likely to provide an environment where Legionella bacteria can grow.
Where conditions are favourable (i.e. suitable growth temperature range; water droplets (aerosols) produced and dispersed; water stored and/or recirculated; some 'food' for the organism to grow such as rust, sludge, scale, biofilm etc) then the bacteria may multiply thus increasing the risk of exposure. It is a simple fact that the organism will colonise both large and small systems so both require risks to be managed effectively.
What you must do
The practical and proportionate application of health and safety law to landlords of domestic rental properties is that whilst there is a duty to assess the risk from exposure to Legionella to ensure the safety of their tenants, this does not require an in-depth, detailed Legionella risk assessment. The risks from hot and cold-water systems in most residential settings are generally considered to be low owing to regular water usage and turnover. A typical ‘low risk’ example may be found in a small building (e.g. housing unit) with small domestic-type water systems, where daily water usage is inevitable and sufficient to turn over the entire system; where cold water is directly from a wholesome mains supply (no stored water tanks); where hot water is fed from instantaneous heaters or low volume water heaters (supplying outlets at 50 °C); and where the only outlets are toilets and wash hand basins.
A simple assessment may show that there are no real risks and are being properly managed and no further action is needed. It is important to review the assessment in case anything changes in the system.
In most cases, the actions landlords need to take are simple and straightforward so compliance does not need to be burdensome or costly. Most landlords can assess the risk themselves and do not need to be professionally trained or accredited; but if they do not feel competent, or inclined to do so, they can arrange for someone who is to do it on their behalf. Most landlords are able to understand the set of risks of running a hot and cold water system in a way that provides the above conditions; and would also be able to implement cheap, simple and effective physical control measures required to minimise the risk of the system becoming colonised with Legionella and other microorganisms.