For most domestic hot and cold water systems, temperature is the most reliable way of minimising the risk of exposure to Legionella. The bacteria multiply where temperatures are between 20-45°C and nutrients are available and are dormant below 20°C and do not survive above 60°C. Put simply, make sure you keep the hot water hot (e.g. above 60°C) and the cold water cold (below 20°C)
2. System design
The kind of water delivery and storage system installed in a building also helps to determine the risk of Legionella contamination. For instance, instantaneous water heaters (such as a combi boiler or electric shower) reduce the risk as there is no water storage.
3. Water storage
Where there is a water storage tank e.g. in a loft space, it’s important for it to be covered with a properly-fitting lid to avoid debris or animal matter getting into the water. In general, water storage should be kept to a minimum i.e. just enough for one day’s usage. If your system has multiple tanks, ensure they are linked together so that water flows through each, avoiding stagnation in any one tank. You can find more information about different water storage systems and their associated risks here.
4. Visual inspection
Careful visual inspection of tanks and pipework will quickly reveal any rusting, cracks or other external damage. Any problems reported by tenants should be attended to promptly to minimise risks (as well as to reduce the cost of any remedial work before the problem worsens).
5. Dead legs
So-called ‘dead legs’ in your plumbing system – pipes leading to an outlet through which water flows but where the outlet is rarely or never used – can also harbour bacteria so represent an increased risk. Where possible dead legs should be removed or capped off.
Other areas to consider with pipework include avoiding long runs of pipes where water could stagnate, insulating hot water pipes to help maintain high temperatures during water transfer and removing any dead ends in the pipework.
7. Revisit your risk assessment
It is advisable to revisit your Legionella risk assessment between tenancies and whenever any significant work is done on the plumbing system. Under any circumstances, a full risk assessment should be carried out at least every two years.
8. Vacant property
A vacant property can lead to water stagnation as the plumbing system isn’t being used. If you have a property standing empty, taps should be run and toilets flushed regularly (ideally weekly) to ensure proper flow-through.
9. Tenant liaison
It’s important to work with your tenants to ensure that they are aware of any control measures in place. For instance, they should be advised not to adjust the temperature setting of the calorifier and to inform you if they notice inconsistent water temperatures. They should also be asked to clean and disinfect shower heads regularly.
10. High risk tenants
Certain groups of people are at higher risk of contracting Legionnaires’ disease so some tenants will be more susceptible than others. The risk increases with age but those at higher risk include people over 45 years of age; smokers and heavy drinkers; people suffering from chronic respiratory or kidney disease, diabetes, lung and heart disease; anyone with an impaired immune system.