Legionella FAQs

Legionnaires’ disease is a potentially fatal form of pneumonia caused by the bacteria Legionella. Legionella grows in water and systems where water is maintained at a temperature to encourage bacterial growth such as cooling towers, hot and cold water systems and spa pools.

It is a legal requirement for landlords, employers and those in control of premises (Duty Holder) to ensure a suitable and sufficient legionella risk assessment is conducted.

The assessment should be undertaken by a ‘competent person’ appointed by the Duty Holder. The activity can be delegated to an employee or outsourced to a contractor. The Duty Holder remains responsible for the management of Legionella. The Approved Code of Practice (ACoP) L8 ‘The control of legionella bacteria in water systems’ describes the duties of landlords, employers and those in control of premises and water systems.

To test for legionella, you can either order kits online to collect a water sample and send it back in the post for testing, or you can appoint someone competent gather samples and have them tested at an approved laboratory. Generally it is best to appoint a competent person or organisation to undertake the activity and interpret the findings for the Duty Holder.

Landlords have a duty to ensure the risk of Legionella exposure is controlled and monitored. The Approved Code of Practice (ACoP) L8 ‘The control of legionella bacteria in water systems’ describes that landlords need to undertake a detailed risk assessment and have an effective monitoring regime in place.

Our Legionella Awareness Training provides landlords and employers with the knowledge to identify and reduce the risks associated with legionella bacteria.

It is recommended that a legionella risk assessment is reviewed in line with the findings of the original risk assessment or sooner if any major changes have happened to the water system in the building or established through monitoring the system and controls in place.

Legionella bacteria can begin to develop in water within 2-3 days if conditions are favourable, such as water temperatures between 20°C and 45°C, stagnation, and the presence of nutrients like biofilm, rust, or organic matter.

Regular monitoring and maintenance are essential to prevent growth.

Legionella bacteria are killed at water temperatures of 60°C or higher. To control the risk, hot water systems should be maintained at 50°C or above throughout the system, ensuring that the temperature reaches at least 60°C during disinfection processes.

A legionella risk assessment is a legal requirement under the Health and Safety at Work etc. Act 1974 and Control of Substances Hazardous to Health Regulations 2002 (COSHH). It identifies and evaluates risks of legionella bacteria growth in water systems, such as hot and cold-water systems or cooling towers.

The assessment includes inspecting system design, temperature control, water stagnation, and maintenance practices, providing recommendations to mitigate the risk of Legionnaires’ disease.

Legionella bacteria are killed at temperatures of 60°C or higher. To prevent growth, hot water should be stored at a minimum of 60°C and distributed at 50°C or above. Regular temperature monitoring and system maintenance are essential for effective control.

Legionella testing frequency depends on the type and complexity of the water system, but for most systems, water temperature checks should be conducted monthly.

Comprehensive risk assessments are typically required every two years or sooner if changes occur. In higher-risk systems, such as cooling towers or spa pools, testing may need to be carried out more frequently as part of ongoing monitoring.

A legionella risk assessment must be carried out by a competent person with the necessary skills, knowledge, and experience to identify and assess legionella risks. This could be an in-house professional with appropriate training or an external specialist with expertise in water systems and legionella control, as defined under the Approved Code of Practice L8 (ACoP L8).

Yes, a legionella risk assessment is a legal requirement under the Health and Safety at Work etc. Act 1974 and the Control of Substances Hazardous to Health Regulations 2002 (COSHH) if you manage premises with a water system.

This applies to landlords, employers, and property managers to ensure the risk of legionella bacteria growth is assessed and controlled to prevent Legionnaires’ disease.

Legionella bacteria in water is caused by conditions that promote their growth, such as stagnant water, temperatures between 20°C and 45°C, the presence of biofilm or organic material, and poor maintenance of water systems.

Common sources include hot and cold-water systems, cooling towers, and poorly cleaned storage tanks. Proper temperature control and regular system maintenance help prevent their development.

Legionella bacteria are naturally occurring microorganisms found in freshwater environments, such as lakes and rivers. They can become hazardous when they grow and spread in man-made water systems, such as cooling towers, hot and cold-water systems, and spa pools.

Inhalation of water droplets containing legionella can cause Legionnaires’ disease, a potentially severe form of pneumonia.

The ideal temperature range for legionella growth is between 20°C and 45°C, with optimal growth occurring around 35°C to 40°C.

Below 20°C, the bacteria remain dormant, and above 60°C, they are killed.

Controlling water temperatures outside this range is key to preventing legionella proliferation.

No, legionella bacteria cannot be spread from person to person. Legionnaires’ disease is contracted by inhaling water droplets or mist contaminated with the bacteria, usually from sources like cooling towers, hot tubs, or water systems. There is no evidence of direct human-to-human transmission.

Yes, chlorine can kill legionella bacteria when used at the correct concentration and contact time.

Maintaining adequate levels of chlorine in water systems, typically between 0.5 and 1 mg/L, is an effective way to control legionella growth.

Regular monitoring and maintenance are essential to ensure chlorine remains effective in preventing contamination.

Yes, a legionella risk assessment is mandatory under the Health and Safety at Work etc. Act 1974 and the Control of Substances Hazardous to Health Regulations 2002 (COSHH).

Employers, landlords, and those in control of premises with water systems must conduct an assessment to identify and control the risk of legionella bacteria, ensuring compliance with the Approved Code of Practice L8 (ACoP L8).

Legionella testing is not a blanket legal requirement, but it may be necessary depending on the outcome of a legionella risk assessment.

For high-risk water systems, such as cooling towers and spa pools, regular testing is often required under the Approved Code of Practice L8 (ACoP L8) to ensure effective control. For low-risk systems, routine monitoring, such as temperature checks, may suffice to meet legal obligations.

There is no universally defined “safe” level of legionella bacteria, as any detectable presence in water systems could pose a risk if conditions allow for growth and spread. However, action levels are set in the HSG274 guidance:

• 100 to 1,000 CFU/L: Requires immediate review of control measures.
• Above 1,000 CFU/L: Requires urgent investigation and system disinfection.

Regular monitoring and maintaining water systems help prevent levels from becoming hazardous.

Legionella bacteria naturally occur in freshwater environments like rivers, lakes, and reservoirs. They become a health risk when they grow and spread in man-made water systems, such as cooling towers, hot and cold-water systems, and spa pools.

Conditions like stagnant water, warm temperatures (20°C – 45°C), and the presence of nutrients, such as biofilm and organic material, promote their growth.

No, not everyone can complete a legionella risk assessment. It must be carried out by a competent person with the necessary skills, knowledge, and experience to identify and assess legionella risks, as required under the Approved Code of Practice L8 (ACoP L8).

This could be a trained in-house professional or an external specialist with expertise in legionella control and water systems.

No, legionella bacteria themselves do not have a smell. However, water systems harbouring legionella may develop unpleasant odours due to stagnant water, biofilm, or organic material, which can indicate poor maintenance and increased risk of contamination. Regular cleaning and monitoring are essential to prevent such issues.

Legionella is contracted by inhaling tiny water droplets or aerosols contaminated with the bacteria. These droplets are typically released from sources such as showers, cooling towers, hot tubs, or other water systems.

Poorly maintained systems with warm, stagnant water provide ideal conditions for legionella growth, increasing the risk of exposure.

Legionella bacteria can survive outside of water for a short period, normally a few hours to days, depending on environmental conditions such as temperature, humidity, and the presence of organic material.

However, they require water and suitable nutrients to grow and multiply, so their survival outside a water environment is limited.

Individuals most at risk of legionella infection, including Legionnaires’ disease, are those with weakened immune systems, adults over 50, smokers, and people with chronic conditions such as lung disease, diabetes, or kidney disease.

Workplace exposure risks are higher for employees in environments with poorly maintained water systems, such as cooling towers, hot tubs, or healthcare facilities.

Legionella bacteria are unlikely to grow in bottled water if it is properly sealed and stored, as the conditions for their growth – warm temperatures (20°C – 45°C), stagnation, and nutrients like biofilm – are not normally present.

However, if bottled water is left open or exposed to heat for extended periods, there is a minimal risk of contamination under the right conditions.

Proper storage in cool environments reduces this risk.

Yes, stagnant water can cause legionella growth. Stagnation creates ideal conditions for the bacteria by allowing water temperatures to stabilise within the range of 20°C to 45°C and enabling the buildup of biofilm and organic material, which provide nutrients for legionella.

Regular flushing and maintenance of water systems are essential to prevent stagnation and reduce the risk.

No, legionella cannot survive in dry conditions.