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Legionella Compliance Method of Work

Legionella Risk Assessments

LRA

A Legionella Risk Assessment is the foundation of effective water safety management. It identifies potential sources of risk in a building’s water system, evaluates how likely Legionella bacteria are to grow and spread, and recommends control measures to protect users from exposure.

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Step 1: Gather Background Information. Before inspecting the site, we collect key information about the premises and its water systems, including:

  • Building layout, schematics and pipework drawings (if available)

  • Types of water systems present (e.g. hot and cold domestic, cooling towers, spa pools)

  • Water usage patterns and occupancy levels

  • Previous Legionella risk assessments and maintenance records

  • Details of any water treatment regimes in place

  • Contact details of the Duty Holder and Responsible Person

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This helps our assessor understand how water is stored, circulated, and used within the property.

 

Step 2:  Site Inspection and System Survey

A full visual and physical inspection of the water systems is carried out to identify potential hazards. This includes:

  • Checking cold-water storage tanks, calorifiers, and hot-water cylinders (safe access will be required)

  • Identifying dead legs, redundant pipework, or low-use outlets

  • Examining shower heads, taps, thermostatic mixing valves (TMVs), and hoses

  • Assessing the condition of tanks (e.g. corrosion, scale, or debris)

  • Reviewing system materials to ensure they are suitable and not supporting bacterial growth

 

We will have ladders to access any loft areas. Removing any excessive equipment/items to enable access would be required.

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Step 3: Temperature Testing and Measurements

Temperature control is a key part of Legionella prevention. The assessor will take temperature readings at various points, such as:

  • Cold water outlets (should be below 20°C after running for 2 minutes)

  • Hot water outlets (should reach at least 50°C within 1 minute)

  • Stored hot water (should be maintained at 60°C or above)

  • Return temperatures on circulation loops

Any deviations from these temperature ranges are recorded as potential risks.

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Step 4: Evaluate System Condition and Risk Factors

The assessor evaluates all findings to determine where and how Legionella bacteria could develop. Risk factors include:

  • Areas of stagnant or low-flow water

  • Inadequate water temperatures

  • Presence of scale, rust, or biofilm

  • Unsuitable materials that support bacterial growth

  • Poorly maintained or unclean tanks and outlets

  • Lack of routine monitoring, cleaning, or flushing

Each risk is rated (e.g. Low, Medium, or High) based on likelihood and potential impact.

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Step 5: Review Management Controls

The assessment also examines management practices and compliance documentation, such as:

  • Existence of a Legionella written scheme of control

  • Evidence of regular temperature checks and flushing regimes

  • Staff training records and awareness levels

  • Maintenance and cleaning schedules

  • Record-keeping systems (paper or digital logbooks)

Any gaps in management or documentation are identified as compliance failures or improvement opportunities.

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Step 6: Report and Action Plan

Our assessor compiles a comprehensive Legionella Risk Assessment Report, including:

  • Description of systems and their condition

  • Identified risks and their severity

  • Photographic evidence (if relevant)

  • Temperature readings and test results

  • Recommended control measures

  • A prioritised action plan for remedial work or improvements

This document provides the evidence base for compliance with HSE ACoP L8 and HSG274 Part 2.

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Step 8: Implementation and Ongoing Monitoring

Once our report is issued, the Duty Holder and Responsible Person must:

  • Implement the recommended control measures

  • Establish a monitoring and maintenance regime

  • Ensure regular flushing, temperature checks, and cleaning

  • Keep records of all actions and inspections

  • Review the risk assessment at least every two years or sooner if system changes occur

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Review and Continuous Improvement

Legionella management is an ongoing process, not a one-time task. Regular reviews ensure that control measures remain effective as buildings, occupancy, and water systems change.

Water Sampling

Sampling

Process for Carrying Out Legionella Water Sampling 

Legionella water sampling is an essential part of monitoring and verifying control measures within water systems. It helps confirm whether the system is under control or if further action is required to reduce the risk of Legionella bacteria.

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Sampling is undertaken by a competent, trained person following HSE guidance (HSG274 Parts 1–3), the Approved Code of Practice (ACoP L8), and relevant BS EN ISO standards to ensure accuracy and validity.

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3. Prepare Sampling Equipment

We ensure all sampling equipment is sterile, clean, and approved for microbiological use. Our equipment typically includes:

  • Sterile sample bottles containing sodium thiosulfate (to neutralise residual disinfectants like chlorine)

  • Calibrated digital thermometer

  • Clean gloves and appropriate PPE

  • Labels or barcodes for sample identification

  • Cool box or temperature-controlled carrier for transport

  • Sample collection forms and chain-of-custody documentation

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Confirm that all equipment complies with BS 7592:2022 – Sampling for Legionella bacteria in water systems.

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4. Carry Out the Sampling

Each sample will be collected carefully to ensure it accurately represents the water conditions at the point of collection.

a. Record Preliminary Data

Before we collect the sample, we:

  • Record the outlet temperature (both immediate and stabilised).

  • Document the location and description of the outlet.

b. Collect the Sample

We will always follow the correct procedure depending on the purpose of the test:

  • Pre-flush sample: Taken immediately after opening the tap to assess actual exposure risk to users.

  • Post-flush sample: Taken after running water for a set time (typically 1–2 minutes) to check system water quality.

Fill the sterile bottle to the indicated level without touching the inside of the cap or bottle. Reseal immediately after collection.

c. Maintain Hygiene

We will use gloves, avoid contamination, and ensure samples are handled aseptically. Each 1 litre bottle should be clearly labelled with:

  • Site name and address

  • Sampling point ID

  • Date and time of sampling

  • Sample type (pre-flush/post-flush)

  • Collector’s initials

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5. Transport Samples to an Accredited Laboratory

Samples will be sent as soon as possible (preferably within 24 hours) to our partnered UKAS-accredited laboratory for Legionella testing.

  • Store samples in a cool box (ideally 2–8°C) during transport.

  • Ensure the laboratory is accredited to ISO/IEC 17025 for Legionella testing.

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6. Laboratory Analysis

At the lab, samples are analysed using culture methods (in accordance with BS EN ISO 11731) to determine if Legionella bacteria are present and, if so, at what concentration (expressed as colony-forming units per litre – cfu/L).

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7. Review and Interpret Results

Once the results are received:

  • Compare them against the HSE guidance thresholds:

Legionella Count (cfu/L)Recommended Action

<100 cfu/LSystem under control – continue routine monitoring

100–999 cfu/LReview control measures and resample to confirm effectiveness

≥1000 cfu/LImmediate investigation, disinfection, and remedial action required

  • Review findings in context of recent maintenance, temperature logs, and risk assessment data.

  • Document all results, actions, and communications.

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8. Take Corrective Actions (If Needed)

If Legionella bacteria are detected:

  1. Notify the Responsible Person immediately.

  2. Investigate the cause (e.g., temperature failure, stagnation, contamination).

  3. Disinfect the system — thermal or chemical treatment as appropriate.

  4. Re-sample after remedial works to confirm effectiveness.

  5. Update the Legionella risk assessment and written scheme of control.

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9. Record Keeping and Reporting

Maintain detailed records of:

  • Sampling plans and locations

  • Results and laboratory certificates

  • Remedial actions taken

  • Updated monitoring schedules

  • Communication with duty holders or enforcement bodies

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Records should be kept for at least five years as evidence of compliance.

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10. Ongoing Monitoring

Legionella sampling is not a one-off exercise — it should form part of a planned water hygiene monitoring programme. Regular review and re-sampling ensure the system remains safe and compliant over time.

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We will always discuss the outcome of any Legionella sampling and provide support for any ongoing corrective actions.

Cold Water Storage Tank Cleaning & Disinfection Works

CWST C&D

Process for Carrying Out a Cold Water Storage Tank Clean and Disinfection

A clean and disinfection of a cold-water storage tank is a key part of Legionella control and general water hygiene management. It removes accumulated sediment, scale, and biofilm, and ensures the stored water remains clean, safe, and compliant with legal requirements.

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The process is carried out by competent, trained personnel following the proper safety and disinfection procedures.

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1. Preparation and Pre-Cleaning Checks

a. Risk Assessment and Method Statement Before starting any work:

  • Review the Legionella risk assessment and method statement.

  • Conduct a site-specific risk assessment to identify hazards such as confined space, electrical risks, or working at height.

  • Ensure all operatives are trained, authorised, and wearing appropriate PPE (gloves, goggles, respirators, protective clothing).

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b. Notify Users

Please Inform all building occupants that the water supply will be isolated and that tanks will be temporarily out of service.

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c. The Equipment That We Will Be Using:

  • Chlorine-based disinfectant (e.g. Hydrogen Peroxide or Chlorine Dioxide)

  • Hoses, brushes, buckets, and wet vacs

  • Clean rags and non-abrasive pads

  • Sterile sample bottles (for post-disinfection sampling, if required)

  • Chlorine test kit

  • Warning signage and barriers

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d. Isolation and Draining

  • Isolate the inlet valve to the tank.

  • Open the drain valve or flush outlets to empty the tank safely and completely.

  • Ensure all connected outlets (e.g. taps, showers) are isolated to prevent contaminated water from entering the system during cleaning.

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2. Visual Inspection and Assessment

Before cleaning, we'll inspect the tank for:

  • Corrosion or damage to the structure or coating

  • Accumulated sediment, scale, or organic debris

  • Signs of biofilm, algae, or microbial growth

  • Condition of lids, vents, and screens (must be intact and insect-proof)

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If the tank is damaged, corroded, or lacks a tight-fitting lid, report this to the Responsible Person — the tank may need repair or replacement before returning to service.

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3. Physical Cleaning

  • Manually scrub the internal surfaces of the tank using clean, non-metallic brushes or pads to remove dirt, sediment, and scale (as far as reasonably practicable).

  • Use minimal water to avoid unnecessary waste.

  • Remove all debris using a wet vacuum or by flushing to drain.

  • Rinse thoroughly with clean water to ensure all contaminants are removed.

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4. Disinfection Procedure

Once the tank is clean, disinfect it using an appropriate biocide.

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a. Prepare the Disinfectant (Hydrogen Peroxide)

Prepare a solution to achieve a minimum of 750 mg/L (ppm) of free chlorine in the tank water. Always follow the manufacturer’s safety instructions and dosing guidelines.

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b. Fill and Circulate (Only if the cleaning includes the down services)

  • Refill the tank with clean water and add the disinfectant to achieve the target biocide concentration.

  • Ensure the tank is filled evenly and the disinfectant is well mixed.

  • Draw disinfected water through all connected outlets until the disinfectant is detected at the farthest point.

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c. Contact Time

We'll maintain a minimum contact time of one hour.
During this time:

  • Ensure all connected outlets remain closed.

  • Check chlorine levels periodically to maintain the target concentration.

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5. Flushing and Recommissioning

After the contact period:

  1. Drain the tank completely.

  2. Flush the system with clean mains water until the chlorine residual is less than 0.5 mg/L (ideally 0).

  3. Refill the tank with clean mains water.

  4. Reopen the isolation valves and restore supply to the system.

  5. Confirm that all outlets are functioning correctly and that the water is clear and free of odour.

 

6. Post-Disinfection Verification

​We'll produce a job sheet and document all activities, including:

  • Date and time of clean/disinfection

  • Operatives’ names and signatures

  • Disinfectant type and concentration

  • Contact time

  • Chlorine residuals before and after flushing

  • Observations and photographs

  • Any defects or remedial recommendations

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You must retain records for at least five years as part of your Legionella control logbook.

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7. Final Inspection and Handover

Before we sign off, we'll:

  • Check that lids, screens, and insulation are in good condition.

  • Ensure warning labels and identification tags are in place.

  • Confirm that water is restored and safe for use.

  • Provide a certificate of clean and disinfection to the Responsible Person or Duty Holder.

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8. Frequency of Cleaning and Disinfection

Cold water storage tanks should be:

  • Inspected annually for cleanliness and condition.

  • Cleaned and disinfected at least every 12 months, or sooner if:

    • The tank is visibly dirty or contaminated.

    • System alterations or maintenance work have occurred.

    • Routine inspection or sampling indicates bacterial contamination.

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Please note that the process may differ depending on the complexity of the system and other factors that may affect the process above.  Please give us a call to discuss any specific requirements.

TMV (Thermostatic Mixing Valve) Servicing & Failsafe Checks

TMV Servicing

Process for Carrying Out TMV Servicing

Thermostatic Mixing Valves (TMVs)** are safety devices installed on hot water outlets to control water temperature and prevent scalding. They blend hot and cold water to a safe, pre-set temperature — typically between 41°C and 43°Cfor handwashing outlets. However, because TMVs mix water and can retain warmth, they can also create ideal conditions for Legionella bacteria if not properly maintained.


Regular TMV servicing is therefore essential to ensure that there are safe outlet temperatures, consistent operation and response and compliance with HSE and Legionella control requirements

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1. Preparation and Pre-Service Checks

a. Review Documentation

  • Review the site’s Legionella risk assessment and asset register to identify all TMVs that require servicing.

  • Check previous service and calibration records to note any recurring issues.

b. Risk Assessment and Safety Precautions

  • Conduct a site-specific risk assessment.

  • Ensure the area is safe to work in and signage is in place (e.g., “Do Not Use Tap – Maintenance in Progress”).

  • Use appropriate PPE: gloves, goggles, and protective clothing.

  • Confirm that isolation valves for both hot and cold feeds are accessible and operational.

c. Tools and Equipment Required

  • Calibrated digital thermometer

  • Thermostatic valve service kit and manufacturer’s tools

  • Cleaning brushes

  • Descaling and disinfectant solution (WRAS-approved)

  • Replacement parts (O-rings, filters, check valves, seals)

  • Towels or absorbent cloths

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2. Isolate and Disassemble the TMV

  1. Isolate the hot and cold water supplies feeding the TMV.

  2. Open the outlet to release any residual pressure.

  3. Remove the TMV cover and internal cartridge according to the manufacturer’s instructions.

  4. Inspect all components for scale, corrosion, or damage.

  5. Carefully remove and retain O-rings, filters, and check valves for cleaning or replacement.

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3. Clean and Descale Components

  • Immerse filters, strainers, and internal components in a WRAS-approved descaling and disinfection solution to remove lime scale and biofilm.

  • Gently scrub with a soft brush — do not use abrasives or metal tools.

  • Rinse all parts thoroughly with clean water to remove any chemical residue.

  • If parts are damaged or excessively worn, replace them with manufacturer-approved components.

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4. Reassemble and Flush

  1. Refit the cleaned (or replaced) components and reassemble the TMV in accordance with the manufacturer’s guidelines.

  2. Slowly open the isolation valves to refill the valve.

  3. Flush the TMV and outlet for several minutes to remove any air and debris.

  4. Check for leaks and ensure water is flowing freely.

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5. Functional Testing and Calibration

After reassembly, verify that the TMV is blending correctly and maintaining safe outlet temperatures.

a. Test Procedure

  1. Allow the outlet to stabilise.

  2. Measure and record the mixed outlet temperature — it should typically be:

    • 41°C ± 2°C for handwash basins

    • 43°C ± 2°C for showers and baths (site-specific)

  3. Simulate a hot and cold water failure test:

    • Isolate the cold supply briefly – the TMV should shut down flow rapidly to prevent scalding.

    • Isolate the hot supply – the TMV should prevent cold water passing back through the valve.

  4. Reopen both supplies and confirm the outlet returns to the correct temperature.

b. Adjustment

If the outlet temperature is outside tolerance, adjust the TMV according to the manufacturer’s instructions using the adjustment spindle or locking cap.

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6. Record Results and Compliance Data

All findings must be accurately recorded, including:

  • TMV identification number and location

  • Pre- and post-service temperatures

  • Details of parts cleaned or replaced

  • Functional test results

  • Date, engineer’s name, and signature

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All of the information will be sent via a job sheet from our Compliance Department.

 

7. Recommission and Handover

  • Confirm all outlets are working correctly and water supply is fully restored.

  • Remove all signage and equipment.

  • Notify the Responsible Person that the TMVs have been serviced and are safe for use.

  • If any faults or non-conformances remain, report them immediately and recommend corrective actions.

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8. Frequency of TMV Servicing

According to HSG274 Part 2 and HTM 04-01 (for healthcare):

  • TMV performance checks should be carried out at least annually (or every 6 months in healthcare and high-risk environments).

  • Full internal cleaning, descaling, and servicing should occur at least once every 12 months.

  • Outlets serving vulnerable users (schools, care homes, healthcare) may require 6-monthly testing.

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