Legionella Services

Legionella is a genus of bacteria found naturally in freshwater environments. The species Legionella pneumophila is responsible for the vast majority of Legionnaires' disease cases in the UK. The bacteria enter building water systems through the mains supply and can multiply rapidly when water temperatures are between 20 and 45 degrees Celsius, nutrients are available (scale, sediment, biofilm, rust), and water is stagnant or slow-moving.

Infection occurs when a person inhales fine water droplets (aerosol) containing Legionella bacteria. Common sources of aerosol include showers, taps (especially spray taps), cooling towers, spa pools, decorative water features, and air conditioning systems that use water. Legionella is not transmitted from person to person, and drinking contaminated water does not cause infection in healthy individuals.

Legionnaires' disease causes severe pneumonia with symptoms including high fever, cough, shortness of breath, muscle aches, and headache. It requires hospitalisation and antibiotic treatment. The fatality rate is approximately 10 to 15 percent overall, and higher among vulnerable groups.

Our Legionella risk assessment is a thorough, systematic evaluation of your water systems against the requirements of ACOP L8 and the technical guidance in HSG274.

The assessment covers identification of all water systems on the premises (hot water, cold water, cooling systems, spa pools, and any other systems that store or distribute water), evaluation of the water system design, age, materials, and condition, identification of specific risk features including dead legs, blind ends, infrequently used outlets, storage tanks, calorifiers, and mixing valves, temperature measurements at key points throughout the hot and cold water systems, assessment of the people at risk, including employees, visitors, residents, and particularly vulnerable groups, review of existing control measures, monitoring records, and maintenance procedures, and a schematic drawing or description of the water system layout.

The assessment produces a written report containing the findings, a risk rating for each element of the system, and specific recommendations for remedial action prioritised by urgency. This report is your primary compliance document and must be kept available for inspection by the HSE or local authority.

Temperature monitoring is the most important ongoing control measure for Legionella risk. Maintaining hot water above 60 degrees Celsius at the storage point and above 50 degrees Celsius at outlets, and cold water below 20 degrees Celsius, keeps water outside the Legionella growth range.

Our monitoring programme includes monthly temperature checks at sentinel outlets (the nearest and furthest outlets from each hot water storage vessel), quarterly checks at all other hot and cold water outlets, regular checks on hot water storage temperatures (calorifier thermostats), cold water storage tank temperature checks, and recording of all results in a monitoring log available for inspection.

We can also install connected temperature sensors that monitor water temperatures continuously and send alerts if temperatures drift outside safe ranges. This provides 24/7 surveillance that is impossible to achieve with manual monitoring alone.

Summer (June to August) - Peak risk: Legionella risk is at its highest during summer when ambient temperatures push cold water systems above the critical 20°C growth threshold. Cold water storage tanks in lofts and roof spaces are particularly vulnerable to solar heating. Water temperatures in the 20-45°C range create ideal conditions for Legionella bacteria to multiply rapidly. Schools, offices, and commercial premises in Darlington, Middlesbrough, and across the North East should increase monitoring frequency during this period.

Autumn (September to November) - Post-holiday risk: Water systems in premises that were closed or had reduced occupancy during the summer holidays pose a significant Legionella risk when they return to full use. Stagnant water in unused outlets, dead legs, and little-used showers can harbour dangerous bacterial levels. Schools, universities, and seasonal businesses should carry out a thorough flushing regime before reopening.

Winter (December to February) - Reduced but present risk: Cold water temperatures generally remain below the 20°C growth threshold during winter, reducing (but not eliminating) the risk. Hot water systems remain a year-round concern - calorifiers, hot water cylinders, and distribution pipework must maintain temperatures above 60°C at all times. Mixed-use properties with complex water systems require ongoing monitoring regardless of season.

Spring (March to May) - Pre-summer preparation: Water system risk assessments and temperature monitoring should be reviewed ahead of the summer risk period. This is the best time to address any remedial actions identified during the previous year's assessment - flushing dead legs, servicing TMVs, cleaning calorifiers, and checking cold water storage tank insulation. Proactive compliance prevents the reactive scramble when temperatures rise.

Landlords have the same legal duties as other duty holders under ACOP L8. This applies to landlords of both commercial and residential rental properties.

For residential rental properties, landlords must carry out a Legionella risk assessment before letting the property and keep the assessment up to date (reviewed at least every two years or when the property or tenancy changes). In most domestic properties with standard combi boilers or system boilers and no water storage tanks, the risk assessment is straightforward and the risk is typically low.

For properties with stored water (cold water tanks in lofts, hot water cylinders), the assessment must consider whether temperatures are maintained outside the growth range, whether outlets are all in regular use, and whether the system is kept clean and in good repair.

For housing associations and portfolio landlords, we provide bulk assessment services covering multiple properties with consolidated reporting and a scheduled review programme.

When our risk assessment or monitoring identifies issues requiring action, we provide clear recommendations and can carry out or coordinate the necessary remedial work.

Common remedial actions include removing or regularly flushing dead legs, adjusting calorifier and hot water storage temperatures, replacing failed thermostatic mixing valves, installing cold water tank lids, insulation, and screening from heat sources, implementing flushing regimes for infrequently used outlets, carrying out thermal or chemical disinfection of contaminated systems, and upgrading pipework or system components to reduce risk.

All remedial work is documented and the risk assessment is updated to reflect the changes. We provide ongoing monitoring to confirm that the corrective actions are effective and that control measures are being maintained.