Water systems and legionella compliance

Your legionella duties

Legionella bacteria can grow in water systems and cause Legionnaires' disease, a potentially fatal form of pneumonia. As an employer, landlord, or person in control of premises, you have a legal duty to assess and control the risk of legionella exposure.

This duty applies to all business premises with a water system - which in practice means every workplace. Even a simple system with a hot water tank and a few taps needs a risk assessment. The requirement comes from the Health and Safety at Work etc. Act 1974, supported by the HSE's Approved Code of Practice L8 (Legionnaires' disease: the control of legionella bacteria in water systems).

Failing to control legionella risk can result in serious illness or death, HSE prosecution, and unlimited fines.

Who needs a risk assessment

You need a legionella risk assessment if you are:

• An employer with any workplace premises
• A landlord (commercial or residential)
• A person in control of premises where water is used or stored

Your risk assessment must be carried out by a competent person. For simple systems (small office with a hot water tank, cold water mains, and a few outlets), a competent member of staff may be able to do the assessment. For larger or more complex systems (cooling towers, spa pools, large buildings with dead legs or stored water), you should use a specialist water treatment company.

HSE's Approved Code of Practice (L8) sets no fixed review interval. You must review the assessment regularly, and whenever there is reason to think it is no longer valid, such as changes to the water system or building use, control measures failing, or a case of Legionnaires' disease.

Temperature management

Legionella bacteria thrive between 20 and 45 degrees Celsius. Temperature control is the most important measure for preventing bacterial growth in your water system.

Hot water

• Store hot water at 60 degrees Celsius or above in the calorifier (hot water cylinder). This temperature kills legionella bacteria.
• Hot water should reach outlets at 50 degrees Celsius or above within one minute of running the tap. If it takes longer, the system may have dead legs or poor insulation.
• Where vulnerable people use the premises, such as care homes and nurseries, fit thermostatic mixing valves (TMVs) at the point of use to limit delivery to 43 degrees Celsius or below while still storing water at 60 degrees Celsius.

Cold water

• Keep cold water below 20 degrees Celsius, ideally below 15 degrees Celsius.
• Insulate cold water pipes that run through warm spaces, and avoid routing them near hot pipes or through boiler rooms.
• Cover cold water storage tanks with close-fitting, insect-proof lids and keep them away from heat sources.

Monthly temperature monitoring

Check water temperatures at representative sentinel outlets each month:

• Hot water at the nearest and furthest outlets from the calorifier
• Cold water at the nearest and furthest outlets from the incoming mains
• Record all readings in a temperature log

If temperatures fall outside the safe ranges, investigate and correct promptly. Persistent temperature problems indicate a system issue that needs professional attention.

Flushing and maintenance regimes

Regular flushing and maintenance prevent water from stagnating and bacteria from colonising your system.

Weekly tasks

Run any tap, shower or other outlet that is not used at least weekly for a minimum of two minutes. This includes outlets in unoccupied rooms, fire hose reels (where accessible) and seasonal facilities. Keep a log of which outlets were flushed and when.

Quarterly tasks

Remove, clean and descale showerheads and hoses, because biofilm and scale in them create ideal conditions for legionella. Replace any showerhead that cannot be cleaned properly. If thermostatic mixing valves are fitted, check they are working correctly.

Annual tasks

• Review the risk assessment and update it if circumstances have changed.
• Inspect cold water storage tanks for contamination and corrosion, and check the lids are secure and insect-proof.
• Clean and disinfect the system if your risk assessment or water treatment provider recommends it.
• Drain, inspect and, if necessary, clean calorifiers.

Record keeping and penalties

Good records show you are complying and help you run your water safety programme. Keep your current risk assessment and earlier versions that show its review history, your written scheme of control, monthly temperature logs from sentinel outlets, weekly flushing logs, maintenance records (showerhead cleaning, tank inspections and disinfection), and evidence that the responsible person has had legionella awareness training.

The HSE enforces legionella duties. Prosecution for failing to manage legionella risk can result in unlimited fines. Where Legionnaires' disease has occurred due to negligence, individual directors and managers may face personal prosecution and imprisonment. In 2023, a hotel company was fined over £500,000 after a guest contracted Legionnaires' disease from a poorly maintained water system.