Legionella Prevention and Control

Preventing Legionnaires' disease starts with controlling Legionella bacteria in water systems. Whether you manage a care home, rental property, hotel, school, or workplace, implementing effective control measures is essential for safety and compliance.

This guide covers the key prevention strategies recommended by UK health and safety authorities.

Water Temperature Control

Temperature is one of the most important factors in controlling Legionella growth. The bacteria thrive between 20°C and 45°C, so maintaining water outside this range is critical.

Hot Water Systems

  • Storage temperature: 60°C or above
  • Distribution temperature: At least 50°C within 1 minute at all outlets
  • Check calorifiers and hot water cylinders monthly
  • Check Sentinel outlets monthly

Cold Water Systems

  • Storage and distribution: Below 20°C
  • Insulate cold water tanks and pipes to prevent warming
  • Keep tanks covered and protected from sunlight
  • Site tanks away from heat sources

Important: The danger zone for Legionella growth is 20–45°C. Water systems that operate within this range require additional control measures.

Regular Flushing

Stagnant water allows bacteria to multiply. Regular flushing prevents stagnation and maintains water quality.

When to Flush

  • Little-used outlets: Weekly flushing for at least 2 minutes
  • After vacancies: Before new occupants move in (rental properties, hotel rooms)
  • After holidays: Schools, offices, and seasonal buildings
  • Dead-legs: Any pipework that doesn't flow regularly

How to Flush Properly

  1. Run hot water first until it reaches maximum temperature
  2. Run cold water until it reaches minimum temperature
  3. Flush for at least 2 minutes per outlet
  4. Keep records of flushing activities

System Design and Maintenance

Avoid Stagnation

  • Remove or regularly flush dead-legs (unused pipe sections)
  • Keep pipe runs as short as possible
  • Ensure good circulation throughout the system
  • Identify and use all outlets regularly

Tank and Water Maintenance

  • Inspect and clean cold water storage tanks annually
  • Ensure tanks have tight-fitting lids
  • Check for debris, sediment, or biofilm
  • Verify insulation is intact and effective
  • Ensure overflow and vent pipes are screened

Descaling and Cleaning

  • Remove scale and sediment from systems regularly
  • Clean showerheads and taps quarterly
  • Descale or replace heavily scaled components
  • Consider water softening in hard water areas

Monitoring and Testing

Temperature Monitoring

  • Check hot water storage monthly (should be 60°C or above)
  • Check hot water at sentinel outlets monthly (should reach 50°C within 1 minute)
  • Check cold water storage monthly (should be below 20°C)
  • Record all temperature readings

Water Testing

  • Test for Legionella bacteria at regular intervals
  • Focus on sentinel outlets and high-risk areas
  • Test after system changes or maintenance work
  • Keep records of all test results

Order Legionella test kits
Read our sampling guide

Risk Assessment

UK law requires duty holders to carry out a Legionella risk assessment. This should:

  • Identify potential sources of risk
  • Assess who might be at risk and how
  • Determine control measures needed
  • Document findings and actions
  • Be reviewed regularly (at least every 2 years or after significant changes)

Request a professional risk assessment

Disinfection and Remediation

If Legionella is detected at elevated levels, you may need to disinfect the system:

Thermal Disinfection

  • Raise hot water temperature to 85°C in the hot water storage tanks (Calorifiers)
  • Flush all outlets for at least 5 minutes
  • Ensure water reaches 60°C at every tap and shower
  • Take precautions to prevent scalding

Chemical Disinfection

  • Use Silver Stabalised Hydrogen Peroxide or other approved biocides
  • Follow manufacturer's instructions carefully
  • Flush thoroughly after treatment
  • Consider professional assistance for complex systems - we can introduce you to a trusted specialist partner if required.

Always retest after disinfection to confirm bacteria levels have been reduced.

Record Keeping

Maintain clear records of all control measures:

  • Risk assessment documents
  • Temperature monitoring logs
  • Flushing schedules and records
  • Water test results
  • Maintenance and cleaning activities
  • System modifications or repairs
  • Training records for responsible persons

Good records demonstrate compliance and help identify trends or problems early.

Who Is Responsible?

Responsibility for Legionella control falls on the duty holder—typically:

  • Building owners
  • Landlords
  • Employers
  • Facilities managers
  • Those in control of premises

The duty holder must appoint a responsible person to manage day-to-day control measures and ensure compliance.

Key Takeaways

  • Keep hot water above 60°C and cold water below 20°C
  • Flush little-used outlets weekly
  • Clean and maintain tanks and systems regularly
  • Monitor temperatures monthly
  • Test water for Legionella at appropriate intervals
  • Keep detailed records of all activities
  • Review risk assessments every 2 years

Effective Legionella control is about consistent, documented action. Simple routine measures can prevent serious health risks and ensure compliance with UK regulations.

Learn about Legionella bacteria
Find out who needs testing
Shop test kits