Legionella FAQs

Here you can find answers to the most frequently asked Water Hygiene and Legionella questions below.

If your query hasn’t been answered give us a call on 01752 270430 or use our contact form and we’ll get back to you as soon as possible.

 Legionella Risk Assessment FAQs

  • Yes, duty holders, including employers and those in control of premises, must ensure the health and safety of their employees or others who may be affected by their undertaking, this includes the risk of legionella. Legionnaires Disease is a form of pneumonia, which can be fatal and the main route of infection is through inhalation, by inhaling airborne water droplets that contain Legionella. This also applies if you are a private Landlord and have rental properties which are occupied.

    This includes taking suitable precautions to prevent, manage and control the risk of exposure to legionella. You can do this by undertaking the following: a risk assessment, actioning all identified risks within the initial report with remedial works, sampling the water quality to confirm bacterial presence with water testing, and carrying out ongoing record keeping also known as monitoring.

    Relevant regulations:

    • Health and safety at work act 1974

    • Managing health and safety at work (reg 3 (1))

    • The water supply (water fittings) regulations 1999

    • Control of substances hazardous to health (COSHH) (reg 6 (1)(a))

    Guidance documents to help you meet regulations:

    • Approved code of practice L8, HSG 274, part 1-3

    If you can prove that you have followed and implemented the guidelines from HSG 274 it is considered that you are meeting the identified regulations listed above.

  • As per the Approved Code of Practice L8 (HSG 274) and in accordance with The Health & Safety at Work Act 1974 states that – “The Duty holder should arrange to review the assessment regularly and specifically when there is reason to suspect it is no longer valid. An indication of when to review the assessment and what to consider should be recorded and this may result from:

    A change to the water system;

    A change to the use of the building where the system is installed;

    New information available about risks or control measures;

    The results of checks indicating that control measures are no longer effective;

    Changes to key personnel;

    A case of legionnaires disease.”

    We recommend annual reviews to ensure correct implementation is being carried out. Legionella bacteria can double within 15 minutes, so it is important to review your risk assessment and monitoring records regularly.

  • Legionella testing, water testing or sampling should not be confused with a legionella risk assessment. Under the Health and Safety at Work Act 1974, Management of Health and Safety at Work, COSHH and a number of other regulations you are required to comply with the HSE’s HSG 274 legionella guidelines.

    Testing or sampling however plays an important role in determining how efficient a water system is managed. The risk assessment may identify that sampling is needed due to existing risks or as a control and management precaution in which case sampling becomes a legal requirement. Without an L8 risk assessment you will not know where and how many samples are required as well as how affective your control and management is. Both these actions should therefore be undertaken to effectively manage your risk from legionella.

    Water testing services include Legionella, e-Coli, total viable count (TVC), Pseudomonas, hard water, chlorine free, pH levels and more.

  • All assessments vary in prices depending on the number of water outlets, cold water storage tanks, hot water cylinders, combi boilers and other water assets that may be present. The number of assets within your water system will determine the time spent on site and how long it will take to produce your report.

    So how much does it cost? Across the industry, prices vary enormously often depending on the size of the company you use and their processes, the speed of works and professionalism. There are two types of assessments, the first is commercial and the second domestic, also referred to as residential rental properties or landlord risk assessments.

    Commercial risk assessments normally start from £250 to in excess of £750, however our prices start from £99 depending on the size of the water system and location.

    Domestic risk assessments can range tremendously with a number of plumbers, gas engineers and other tradesmen offering these assessments without the specialist training, it’s important to check that your assessor or engineer is properly qualified. Our prices start from £55 for multiple landlord properties to £95 for single landlord properties. Our prices for residential rental properties are based on the property being no more than 5 bedrooms.

  • On average, the time our qualified assessor spends on site is 1 hour for every 10 outlets (sinks, showers, baths, etc). So an assessment can take anywhere between 30 minutes to 6 or 7 hours. It entirely depends on the size of your water system and the number of water assets you have such as cold water storage tanks, cylinders or combination boilers.

    Our engineers will work closely with you to ensure minimal disruption to your business is caused. Clear and easy access to rooms and buildings will play a part in time spent on site at your premises.

  • You will receive your LRA report between 2-10 working days from the date the assessment was carried out. From time to time, not often, our team will need a little more time, so please expect to have your report no later than 30 days. Need your assessment sooner? Get your report, guaranteed next day delivery via email for just £50.

  • Within your report document, you will have an action plan offering guidance which lists all identified risks, with photos, that need remedying in order of importance (legionella remedial works). By following our advice and undertaking remedial works you will reduce the risk of exposure to Legionnaires’ disease. Once all the remedial works are complete, you will then need to focus on implementing your legionella monitoring (periodical checks and maintenance) with a logbook for recording keeping all legal duties and monitoring requirements to ensure you are meeting all your legal requirements.

  • As an employer, or a person in control of the premises, you are responsible for health and safety and need to take the right precautions to reduce the risks of exposure to legionella. You must understand how to:

    • identify and assess sources of risk – legionella risk assessment

    • manage any risks – legionella remedial works

    • prevent or control any risks – legionella monitoring

    • keep and maintain the correct records and carry out any other duties you may have – legionella monitoring

Legionella Testing

  • Either:

    >100-1000 cfu/l

    • if the minority of samples are positive, the system should be resampled, if similar results are found again, a review of the control measures and risk assessment should be carried out to identify any remedial actions necessary or

    • if the majority of samples are positive, the system may be colonised, albeit at a low level. An immediate review of the control measures and risk assessment should be carried out to identify any other remedial action required. Disinfection of the system should be considered.

    >1000 cfu/l

    • The system should be resampled and an immediate review of the control measures and risk assessment carried out to identify any remedial actions, including possible disinfection of the system. Retesting should take place a few days after disinfection and at frequent intervals afterwards until a satisfactory level of control is achieved.

  • The HSE’s Approved Code of Practice (ACoP L8) HSG 274, states that you are currently legally required to undertake an l8 risk assessment, where this will recommend is legionella sampling is required.

  • No, these are not the same thing and offer different benefits as part of an overall legionella control strategy. An L8 risk assessment is a legal requirement and helps to identify areas that pose a risk of legionella growth. Whereas legionella testing is not a legal requirement but is the only way to detect presence of legionella in the water system and therefore, plays a crucial role in legionella control. They are two different services for different purposes. Without a legionella risk assessment, legionella testing is carried out without the necessary information to undertake testing accurately.

  • Legionella testing takes 10-14 days, this allows the bacteria to be cultivated and meet requirements set in place by UKAS for the correct bacteria testing conditions. Once the testing is completed the reports are produced by our team thereafter. Results are sent as soon as they become available and have been reviewed.

  • Legionella testing starts from £40.00+VAT for a single bottle. There may be additional charges for site visits, delivery, postage or specialist guidance or advise.

  • No, landlords must undertake a legionella risk assessment in line with the Health and Safety at Work Act 1974. However, as guidelines state for commercial properties, legionella testing is recommended to determine legionella presents or as recommended by the legionella risk assessment, which is required.

  • A legionella certificate is a phrase that is used regularly but it has little meaning. You are required to have a risk assessment in line with the Health and Safety at Work Act 1974, COSHH, Management of Health and Safety at Work Act to name a few. This risk assessment is a live document that should be required periodically as required by law & the guidelines used to state an assessment was required every two years. After a legionella risk assessment you should be issued with a risk assessment report, and after a legionella test you should be issued with a legionella test sample report. Neither of these are certificates. Legionella is a bacteria that must be managed continuously, and therefore a one off certificate is insufficient to prove compliant and control of the bacteria.

  • Generally no. In order to test for legionella you will need experience in growing bacteria in laboratory conditions to specific standards for accurate results.

  • If you are not making money from your property, e.g. letting a property, then the answer is no. There is currently no law to undertake legionella testing in private domestic properties. However, if you provide accommodation or let a property then you are required to ensure you meet all Health and Safety at Work Act 1974.

Legionella Testing kit

  • x1 Sterile Sample Bottle

    x1 Instructions

    x1 Pre-Paid Return Pack

  • It is recommended that you use one sample bottle for each sample point. Do not mix samples from more than one tap as this will dilute positive results and gives no indication of what outlet or area is affected.

  • The bottle must be full, with at least 250ml of water to undertake the test. Refunds will not be offered where minimum sample requirements are not met.

  • We will start analysing your water sample as soon as we receive the bottles. The legionella bacteria culture test tasks at least 10 days to confirm results.

  • C&M Water is a water hygiene specialist, so unlike many other water testing service providers we are not just a laboratory, we’re water hygiene consultants, and therefore can explain what your results mean, and what the next actions are to remove the bacteria from your water system. C&M Water offers disinfection and chlorination services for legionella when detected.

  • Drinking water (including water dispensers and coffee machines)

    Hot and cold water systems

    Care Homes

    Healthcare premises

    Water heaters

    Dental units

    Swimming pools

    Spa baths

    Cooling towers

    Eye showers

    Eye wash units

    Water fountains

    Vending machines

    Closed water systems

  • The DIY test kit is best suited for those who wish for non-intrusive testing of water in areas such as Doctors surgeries or Dental practices. You may also wish to have testing or sampling carried out at home. Alternatively if you’re working on a budget, then this is a great way to reduce costs by undertaking the sampling yourself. Removing the need for water hygiene specialists visiting to perform the sampling for you. Our test kit comes with easy to use instructions with full customer support if required.

  • It is recommended that you use one sample bottle for each sample point. Do not mix samples from more than one tap as this will dilute positive results and gives no indication of what outlet or area is affected. May companies provide sampling at low prices with this formula. It is not recommended and often becomes more expensive should you have a positive result, you will need to pay for more samples.

  • When it comes to testing water, time is of the essence! Once the sample is put into your sample bottle, we have 24 hours to get the test to our laboratories for testing. Any longer and this can make for inaccurate readings.

Legionella Schematic Drawings

  • Legionella Schematic Drawings form an integral part of any legionella control and management programme and are specifically required by the HSE’s guidelines – HSG 274 Part 2. The legionella schematic drawings may be a simplified but accurate diagram that identifies the water system assets and equipment components.

  • A schematic drawing will help display the layout of your water system and will help you to identify risks and monthly temperature points (sentinel points). Key problem areas can be easily be identified and assists engineers in undertaking remedial works and water disinfections when removing any bacteria present.

  • An indication of when to review the schematic:

    A change to the water system;

    A change to the use of the building where the system is installed;

    New information available about risks or control measures;

    The results of checks indicating that control measures are no longer effective;

    A case of legionnaires disease.”

    We recommend annual reviews to ensure correct implementation is being carried out. Legionella bacteria can double within 15 minutes, so it is important to review your report and monitoring records regularly.

  • On average, schematics are drawn within 1-4 hours. These are then sent at the same time as your legionella risk assessment and any other documentation if provided as part of the same service.

    You will receive your legionella schematic drawing between 2-10 working days from the date of the site visit or order. From time to time, not often, our team will need a little more time, so please expect to have your report no later than 30 days.

Legionella Training

  • “The responsible person(s) appointed to implement the control measures and strategies should be suitably informed, instructed, and trained and their suitability assessed.”

    Section 18 – ACOP L8 HSG 274 Part 2 (Fourth Edition 2014)

  • This course is suitable for duty holders and responsible persons for health and safety of buildings with water systems of any size. This includes employers, self-employed and people who control water systems.

    Landlords also have an obligation to be aware of the dangers of legionella and must undertake a legionella risk assessment to identify the risks from legionella.

  • On successful completion of this course will will receive a legionella awareness online training course certificate via email the same working day as completed. This can be used to provide evidence for compliance and auditing.

  • The end of course test is taken after you have read through all of your training course material. You will be asked to complete a multiple choice questionnaire, where you will be marked automatically so you will know instantly whether you have passed. If you don’t pass don’t worry, you can take the test as many times as you need with no further charge.

Legionella Remedial Works

  • After undertaking the legionella risk assessment it will have identified a number of risk areas within your report, that you need to remove or remedy to reduce the risk of exposure to legionnaires disease.

  • You will only need to carry out legionella remedial works once if actioned correctly. Should you make any additional changes to your water system it is important to consult with your water hygiene specialist to ensure the changes meet current regulations. However, legionella monitoring is an ongoing requirement where inspections and monitoring tasks should be carried out throughout the year. Periodic reviews of the legionella risk assessment should also be completed.

  • Yes, you’ll receive a site report with photos of all the completed works. This way you have evidence and proof of works, as opposed to a certificate which is not legally required. We aim to provide you with peace of mind through out customer service and proof of work.

  • By undertaking remedial works you will reduce the risk of exposure to legionnaires disease. Once all the legionella remedial works are complete, you will then need to focus on implementing your legionella monitoring (periodical checks and maintenance) with a logbook for recording keeping all legal duties and monitoring requirements.

  • View our Legionella remedial works page to see a full list of all remedial work services.

  • These regulations are not directly concerned with legionella hazards, but govern the design, construction and use of materials in water systems. They cover:

    • back-flow protection (use of air gaps and non-return valves);

    • the maintenance of water quality (tank designs);

    • the use of materials (those that do not promote bacterial growth);

    • water conservation (prevent leakage).

  • HTM 04-01: Safe water in healthcare premises. Part A: Design, installation and commissioning practices (Table 2 – Page 55)

    Areas where TMV type 3 valves should be fitted:

    • Showers and hair-wash facilities (set to 41°C)

    • Unassisted Baths (set to 41°C)

    • Baths for Assisted Bathing (set to 46°C – to allow for the cold mass of the bath. NB – prior to patient immersion, water should be checked with a thermometer.)

    • Bidets (set to 38°C)

  • HSG 274 Part 2 (Paragraph 2.127 – Page 42)

    Where necessary, hot and cold water services should be cleaned, flushed and disinfected in the following situations, as specified in BS 8558:

    • on completion of a new water installation or refurbishment of a hot and cold water system;

    • on installation of new components, especially those which have been pressure tested using water by the manufacturer (see the manufacturer’s instructions);

    • where the hot and cold water is not used for a prolonged period and has not been flushed as recommended or the control measures have not been effective for a prolonged period. For example, this could be as little as two or three weeks, but will depend on the ambient temperature, condition of the water system, potential for exposure to aerosols and the susceptibility of users considered in a specific risk assessment;

    • on routine inspection of the water storage tanks, where there is evidence of significant contamination or stagnation;

    • if the system or part of it has been substantially altered or entered for maintenance purposes that may introduce contamination;

    • following water sampling results that indicate evidence of microbial contamination of the water system (see Table 2.2 or 2.3);

    • during, or following an outbreak or suspected outbreak of legionellosis linked to the system;

    • or where indicated by the risk assessment.

  • You should ensure all flexible hoses comply with the WRAS approval scheme and be tested and comply with BS 6920. “In buildings where there are those with an increased susceptibility to infection or with processes requiring specific water characteristics, materials of an enhanced quality may be required.

    Healthcare buildings and care homes should specifically take note of alerts and advice from the Department of Health and Health Facilities Scotland. For example, healthcare premises are advised against the use of ethylene propylene diene monomer (EPDM) lined flexible hoses (tails) as these have been shown to be a risk of microbial colonisation. Such flexible connections should therefore only be used in healthcare premises where an installation has to move during operation or is subject to vibration.” – HSE 274 Part 2 p.2.35

    “Flexible hoses should be used only for the following applications: to allow for vibration of equipment; to accommodate vertical displacement of high and low baths and sinks; to facilitate essential maintenance and access of bespoke equipment when no alternative is available. Note – Where fitted, flexible hoses should be kept as short as possible and be kink-free as to no affect flow”. – The Health Technical Memorandum 04-01: Safe water in healthcare premises. Part A: Design, installation and commissioning states in p.3.41

  • “The Regulations require employers to use a safety sign where there is a significant risk to health and safety” – The Health & Safety (Safety Signs and Signals) Regulations 1996 p.4

    Caution signs are recommended at any location where there is the potential for scalding hot water. This includes where TMVs are located as they may fail.

  • “The Regulations require employers to use a safety sign where there is a significant risk to health and safety” – The Health & Safety (Safety Signs and Signals) Regulations 1996 p.4

    Caution signs are recommended at any location where there is the potential for scalding hot water. This includes where TMVs are located as they may fail.

  • ACOPs L8 states that “It is important that there should be ease of access to all parts of the system, components and associated equipment for management and maintenance purposes, e.g. tanks, calorifiers, thermostatic mixing valves (TMVs)…”

    For more information please visit HSEs website for more information about ACOP L8.

Legionella Monitoring (Water Logbook)

  • Legionella Risk Assessment

    The first step in meeting Legionella compliance is to undertake a legionella risk assessment that will identify the potential risks from Legionella posed by your water systems.

    Legionella Remedial Works

    Once these risks have been identified they should be removed, substituted or managed. This means undertaking any remedial works to reduce the risks identified.

    Legionella Monitoring

    Finally, you will need to control and manage the ongoing risk of Legionella exposure from your water system to employees and visitors by carrying out continued legionella monitoring.

  • A water logbook may cost between £50-100 depending on whether you opt for a generic logbook or a bespoke logbook.

    It is high recommended that you have a bespoke logbook made after your legionella risk assessment to correspond with your report. Our research and regular periodic visits show that customers that opt for a bespoke logbook rather than a generic one are 95% more likely to complete their logbook accurately and in accordance to the HSG274 legionella guidelines.

    This means people are safer and compliance is better almost 100% more than those with generic logbooks

  • Under the Health and Safety at Work Act 1974 and in compliance with the Approved Code of Practice (ACoP L8, HSG 274), duty holders, including employers and those in control of premises, must ensure the health and safety of their employees or others who may be affected by their undertaking.

    This includes taking suitable precautions to prevent, manage and control the risk of exposure to legionella. You can do this by undertaking the following: a legionella risk assessment, actioning all identified risks within the risk assessment with legionella remedial works, sampling the water quality to confirm bacterial presence with legionella testing, and carrying out ongoing record keeping also known as legionella monitoring or water monitoring.

    Take our online legionella training course for a better understanding of the compliance needed.

  • Following a legionella risk assessment a water logbook should be produced to aid with your legionella monitoring and record keeping. Each water system is different and therefore will require a bespoke water monitoring plan. Typically tasks should be undertaken weekly, monthly, quarterly, six monthly and annually.

  • Water monitoring prices vary depending on the number of water outlets, cold water storage tanks, hot water cylinders, combi boilers and other water assets that may be present. The number of assets within your water system will determine the time spent on site and how long it will take to carry out all legionella monitoring tasks.

    So how much does a water monitoring cost? Across the industry prices vary enormously often depending on the size of the company you use and their processes, speed of works and professionalism.

    C&M Water carry out price comparison and reviews regularly to ensure our prices are kept competitive and with the customer in mind.

  • Depending on the type of water monitoring visit it is and the size of the water system will determine how long a water hygiene engineer is on site for. For monthly temperature monitoring you can expect the engineer to be on site for a period of 30-60 minutes on average. However, if the tasks are quarterly de-scaling you might expect the engineer to be present for 1-4 hours.

    Other tasks such as TMV servicing and inspections can take considerably longer due to the nature of the works.

  • Legionella monitoring contracts at uRisk range from 2 to 5 years. In special circumstances we offer 12-month contracts, but the longer the contract the better price we can offer you.

  • By opting for remote water monitoring you are choosing to use the industry’s latest technology in automated temperature monitoring, removing the need for manual temperature monitoring. This means reduced man hours spent driving between sites, reduced costs on travel and labour, improved management system with all records online in one place, and easy assess to records. The list really is endless.

    Whilst this is a great technology, it only completes your monthly temperature monitoring. It still means that weekly flushing, quarterly descaling, six monthly expansion vessel flushing and annual tasks, servicing and inspections are still required.

Chlorination and Disinfections

  • HSG 274 part 2 (paragraph 2.127 – page 42)

    Where necessary, hot, and cold-water services should be cleaned, flushed, and disinfected in the following situations, as specified in BS 8558:

    on completion of a new water installation or refurbishment of a hot and cold-water system

    on installation of new components, especially those which have been pressure tested using water by the manufacturer (see the manufacturer’s instructions)

    where the hot and cold water is not used for a prolonged period and has not been flushed as recommended or the control measures have not been effective for a prolonged period. For example, this could be as little as two or three weeks, but will depend on the ambient temperature, condition of the water system, potential for exposure to aerosols and the susceptibility of users considered in a specific risk assessment

    on routine inspection of the water storage tanks, where there is evidence of significant contamination or stagnation

    if the system or part of it has been substantially altered or entered for maintenance purposes that may introduce contamination

    following water sampling results that indicate evidence of microbial contamination of the water system (see Table 2.2 or 2.3)

    during, or following an outbreak or suspected outbreak of legionellosis linked to the system

    or where indicated by the risk assessment

  • A biocide such a chlorine is inputted into your water system when micro-bacteria is present. It is left within the water system at the correct dosage rate for a calculated contact time, normally 1 hour.

    Once the chlorination/disinfection is completed, all chlorine will be removed from the water system through flushing and using a neutralising agent such as sodium thiosulphate.

    During the disinfection process water usage will not be permitted and warning signs are put in place where occupants are present or may be at risk.

  • Once the chlorine or biocide has been neutralised or removed and signs have been taken down, it will be safe to start using the water again from a chemical free water supply perspective. However, micro-bacteria may remain present if the disinfection has been unsuccessful. Therefore it is advised that you speak with your service provider for the best plan of action and/or wait for confirmation from your sampling results for additional cover.

Other FAQs

  • The site population is presumed to be mixed age, smokers may be present, possible for males over 50 to be present and potential for underlying health issues at all sites/properties.

    Potential for aerosol exposure

    The presence of shower heads and spray taps increase the risk of aerosol exposure (spray). As well as fast flow rates from outlets that cause a splash back and lime-scale build-up.

    Potential for Legionella proliferation Dead legs/ ends

    Dead legs/ ends are lengths of pipe work that do not allow water to flow, therefore, increasing the risk of stagnation and legionella growth. E.g., capped pipework where a tap has been removed.

    The HSG 274 part 2: The control of legionella bacteria in hot and cold-water systems state in paragraph 2.166 – “Where reasonably practice, dead legs should be removed, or the risk minimised by regular use of these outlets.”

  • Temperature information:

    all cold water must be below 20°C within 2 minutes of flushing

    hot water should be at least 50°C within 1 minute of flushing

    cylinders should be at least 60°C and return at least at 50°C

    combi-boilers should operate at 50-60°C, as should electric water heaters.

    TMV temperatures should be set to a maximum of:

    41°C for showers

    41°C for washbasins

    44°C for unassisted bath fill

    46°C for assisted bath fill

    Water supplied by TMVs should never exceed 46°C.

    Scalding Temperature

    The ACOP L8 states that ‘there is a risk of scalding where the water temperature at the outlet is above 44°C.

  • These regulations are not directly concerned with legionella hazards, but govern the design, construction and use of materials in water systems. They cover:

    backflow protection (use of air gaps and non-return valves)

    the maintenance of water quality (tank designs)

    the use of materials (those that do not promote bacterial growth)

    water conservation (prevent leakage)

  • ACOPs L8 states that “It is important that there should be ease of access to all parts of the system, components and associated equipment for management and maintenance purposes, e.g., tanks, calorifiers, thermostatic mixing valves (TMVs)…”

    For more information, please visit HSEs website for more information about ACOP L8.

Cooling Towers

  • HSG 274 part 1 (table 1.1 – page 16)

    Microbial activity – as estimated by dip slides or TVCs (total viable counts) at 30°C (minimum 48 hours incubation) Not greater than 1 x 10(4) cfu/ml (colony forming units per milliliters)

    Legionella – Not detected or not greater than 100 cfu/l

    Corrosion of carbon steel – generally less than 5 mpy and preferably less than 2 mpy Scale control

    No significant loss of hardness from solution (e.g., a calcium balance of >0.9)

    Minimal visible deposition of hardness salts on pack or other surfaces and no significant loss of heat transfer efficiency because of deposition

    Physical fouling and system cleanliness

    Bulk water should be visually clear, and the frequency of physical cleaning and disinfection should reflect the tendency of the system to build up fouling deposits because of airborne or process contamination or microbial growth

  • HSG 274 part 1 (table 1.9 – page 42)

    Aerobic count (cfu/ml and dip slide appearance at 30°C for 48 hours incubation) Less than 10,000 (1 x 10(4)) cfu/ml

    System under control: Good general microbial control and no action required More than 10,000 (1 x 10(4) and up to 100,000 (1 x 10(5)) cfu/ml

    Caution: Review programme operation. Ensure the water treatment programme and system operation is operating correctly. Adjust the biocide dosage if appropriate and resample after 24 hours

    More than 100,000 (1 x 10(5)) cfu/ml

    Action – review programme operation and implement corrective action. As a precaution, the system should be shot dosed with an appropriate biocide or the level of continuous dosage of biocide should be increased. The system should then be re-sampled after 24 hours to determine the effectiveness of the corrective action. If the high count persists, the control measures should be reviewed and the risk assessment to identify any necessary remedial actions

  • HSG 274 part 1 (table 1.10 – page 44)

    Legionella bacteria not detected or up to 100 – ‘Not detected’ does not mean ‘not present’ or that there is no risk. Focus on maintaining control measures, particularly keeping the general aerobic count less than 1 x 10(4) cfu/ml

    Legionella bacteria >100 and up to 1000ml – Low-level legionella count detected. This may be a sporadic result or could indicate a persistent problem. Reassess the control programme and the general aerobic count. Ensure the water treatment system is operating correctly.

    Adjust the biocide dosage if the general aerobic count does not indicate good control (less than 1 x 10(4) cfu/ml. resample to verify the initial results and then again to check that remedial actions are effective

    Legionella >1000 or persistent low-level results – Immediate action required. Resample and as a precautionary measure shot dose the water system with an appropriate biocide or increase the level of continuous dosage of biocide

    Reassess the entire control programme and take any corrective actions. Resample the system to verify the count and to determine the effectiveness of the corrective action, resample again within 48 hours. If the high legionella counts persist, review the risk assessment to identify further remedial actions

    Once the water system is colonised with legionella, it may prove extremely difficult to reduce numbers to undetectable levels and periodic positive legionella results may recur. Under such circumstances steps should be taken to make sure the risk assessment reflects this, and control measures should be devised to ensure that, although likely to be present at low levels, legionella cannot multiply to dangerous levels