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.

The assessment must be reviewed at least every two years, or sooner if there are changes to the water system, building use, or following any cases 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

• Storage temperature - hot water must be stored at 60 degrees Celsius or above in the calorifier (hot water cylinder). This temperature kills legionella bacteria.
• Distribution temperature - 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 insufficient insulation.
• Scalding risk - where vulnerable people (care homes, nurseries) use the premises, thermostatic mixing valves (TMVs) should be fitted at the point of use to limit delivery temperature to 43 degrees Celsius or below while maintaining storage at 60 degrees Celsius.

Cold water

• Target temperature - cold water should be below 20 degrees Celsius, ideally below 15 degrees Celsius.
• Insulation - cold water pipes must not run through warm spaces without insulation. Avoid routing cold pipes near hot pipes or through boiler rooms.
• Cold water storage tanks - must be covered with close-fitting, insect-proof lids. Located 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

• Flush little-used outlets - run taps, showers, and other outlets that are not used at least weekly for a minimum of two minutes. This includes outlets in unoccupied rooms, fire hose reels (where accessible), and any seasonal facilities.
• Record flushing - keep a log of which outlets were flushed and when.

Quarterly tasks

• Clean and descale showerheads - remove, clean, and descale showerheads and hoses. Biofilm and scale in showerheads create ideal conditions for legionella growth. Replace showerheads that cannot be adequately cleaned.
• Check TMVs - if thermostatic mixing valves are fitted, check they are operating correctly.

Annual tasks

• Review the risk assessment - confirm it is still valid or update if circumstances have changed.
• Inspect cold water storage tanks - check for contamination, corrosion, and that lids are secure and insect-proof.
• Clean and disinfect the system - if recommended by your risk assessment or water treatment provider.
• Service calorifiers - drain, inspect, and clean if necessary.

Water fittings and plumbing

When installing or modifying water fittings and plumbing in your premises, you must comply with the Water Supply (Water Fittings) Regulations 1999. These regulations prevent contamination and waste of the public water supply.

Unvented hot water systems

If you install an unvented hot water system (a pressurised system connected directly to the mains rather than fed from a cold water storage tank), building regulations require you to notify your local authority building control before installation begins.

Record keeping and penalties

Good records demonstrate your compliance and help manage your water safety programme effectively. You must keep:

• Legionella risk assessment - the current assessment plus previous versions showing review history
• Written scheme of control - your documented plan for preventing and controlling legionella risk
• Temperature monitoring logs - monthly readings from sentinel outlets
• Flushing logs - weekly records of outlet flushing
• Maintenance records - showerhead cleaning, tank inspections, system disinfection
• Training records - evidence that the responsible person has been trained in legionella awareness