6 Common Legionella Risks in Commercial and Residential Properties

Understanding Legionella Risks

Legionella bacteria can thrive in any water system if conditions allow, posing a serious risk of Legionnaires’ disease, a potentially fatal form of pneumonia. Both commercial and residential properties must identify and control Legionella risks to ensure compliance with UK regulations and protect occupants from harm. This blog explores the most common Legionella risks for businesses, landlords, and property managers can mitigate these risks effectively.

1. Stagnant or Little-Used Water Systems

One of the biggest risk factors for Legionella growth is stagnant water. When water sits unused for weeks or months, bacteria can multiply in the system.

High-Risk Scenarios:

• Vacant properties (e.g., rental homes or commercial buildings awaiting tenants)
• Hotel rooms that are rarely occupied
• Rarely used taps, showers, and toilets in offices or large facilities
• Seasonal buildings (e.g., holiday lets, schools during summer breaks)

Prevention Tips:

✔ Flush out little-used outlets at least weekly
✔ Regularly run showers and taps in vacant properties
✔ Consider automatic flushing systems for infrequently used outlets

2. Incorrect Water Temperatures

Legionella bacteria thrive between 20°C and 45°C. If your hot or cold water systems fall within this range, there’s a higher risk of bacterial growth.

High-Risk Scenarios:

• Hot water stored below 50°C (UK law requires hot water to be stored at 60°C+)
• Cold water temperatures exceeding 20°C
• Poor insulation causing fluctuating water temperatures

Prevention Tips:

✔ Keep hot water at 60°C+ and cold water below 20°C
✔ Regularly check and record water temperatures
✔ Ensure proper insulation on pipes to prevent temperature changes

3. Poorly Maintained Water Storage Tanks

Water storage tanks can become a breeding ground for Legionella if they are not properly maintained or cleaned.

High-Risk Scenarios:

• Dirty or corroded tanks with biofilm, rust, or sediment
• Tanks that aren’t properly sealed, allowing contaminants to enter
• Cold water tanks where water is stored above 20°C

Prevention Tips:

✔ Regularly inspect and clean water storage tanks
✔ Ensure tanks are properly sealed and insulated
✔ Remove unused tanks from the system to eliminate stagnant water

4. Biofilm and Scale Buildup in Pipework

Biofilm (a slimy layer of bacteria and microorganisms) can form inside pipework, protecting Legionella from disinfectants and making it harder to control. Limescale can also provide a surface for bacteria to cling to, increasing risk.

High-Risk Scenarios:

• Old pipework with corrosion and rough surfaces
• Hard water areas where limescale builds up quickly
• Infrequent cleaning and poor water system maintenance

Prevention Tips:

✔ Use water softeners in hard water areas to reduce scale
✔ Regularly clean and descale taps, showerheads, and pipework
✔ Implement disinfection treatments to control biofilm growth

5. Cooling Towers, Spa Pools & Water Features

Any aerosol-producing water system (where water droplets become airborne) poses significant Legionella risks, as bacteria can spread through inhalation.

High-Risk Scenarios:

• Cooling towers and evaporative condensers in industrial settings
• Spa pools, jacuzzis, and hot tubs
• Fountains and decorative water features in public spaces

Prevention Tips:

✔ Regularly disinfect and maintain cooling towers and spa pools
✔ Use biocide treatments to control bacteria growth
✔ Follow HSG274 Part 3 guidelines for managing Legionella in water systems

6. Dead Legs and Redundant Pipework

Dead legs (sections of pipe where water does not flow) and redundant pipework create areas of stagnant water, where Legionella bacteria can thrive.

High-Risk Scenarios:

• Old plumbing left in place after renovations
• Unused pipework leading to decommissioned outlets
• Complex water systems with long pipe runs and low flow rates

Prevention Tips:

✔ Identify and remove dead legs in your plumbing system
✔ Ensure all outlets are regularly flushed to prevent stagnation
✔ Design water systems to minimise areas where water can sit unused

How to Reduce Legionella Risk in Your Property

The key to Legionella prevention is proactive water system management. Follow these best practices to keep your water systems safe:

✅ Conduct Legionella risk assessments at least every 2 years (or more frequently if risks change)
✅ Implement a water hygiene management plan
✅ Train staff and duty holders on Legionella control measures
✅ Regularly monitor water temperatures and flush stagnant outlets
✅ Keep records of all inspections, testing, and maintenance activities

Need Expert Help?

At H2O Comply, we provide professional Legionella risk assessments, water system maintenance, and compliance services. If you’re unsure about the risks in your property, get in touch today.

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