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Legionella Temperature Checks

Temperature control and legionella bacteria prevention

What is legionella bacteria?

Legionella is a bacteria found naturally in water such as rivers and ponds. Given favourable conditions and nutrients to grow, legionella bacteria can colonise man-made water systems. For an outbreak of legionniares’ disease to occur the bacteria must be disseminated in aerosol form and inhaled by a susceptible person. Legionnaires’ disease is a man-made problem and one which is preventable by following the latest HSE guidance.

What temperature kills legionella bacteria?

As with all living things the conditions need to be right for survival and growth to occur and with legionella bacteria temperature is one of the key factors in determining the correct conditions.  There are no known cases of Legionnaires’ disease from natural watercourses such as rivers or streams which in the Uk are typically less than 20°c.
In man-made systems, legionella bacteria require the right conditions to grow and multiply and a vital condition is the temperature must be between 20°c and 45°c.  If the temperature is below 20°c legionella bacteria will lie dormant and when temperatures are above 60°c the bacteria is killed off. 

How hot does water have to be to control legionella bacteria?

Temperature is the most straight forward, cheapest and the most common way in which Legionella bacteria is controlled in domestic hot and cold-water systems. 

Hot water must be stored in hot water cylinders or calorifiers at 60°C or higher to ensure if legionella bacteria were to enter a given water system it would be killed off and not be able to grow and colonise a system.

Hot water should achieve no less than 50°C (55° in health care premises) at the outlets within one minute of running the tap/outlet.

The monthly check of the temperature on the flow of a calorifier must be 60°c.  The temperature of the return pipe must also reach no less than 50°c to ensure the entire system temperature will prevent legionella bacteria from growing.

Direct fired (gas) water heaters are considered to be a lower risk as the volume of stored water is often less than in calorifiers and the temperature is distributed more evenly in the cylinder with less stratification.

How hot do point of use water heaters need to be to control legionella?

POU’s with storage of no more than 15 litres must be checked to ensure they operate between 50° and 60°c. It is important to ensure all POU’s have a high turnover of water so it is not providing a stagnant area of the system. 

Can legionella survive in cold water?

Cold water should be stored and distributed at below 20°C within 2 minutes of running the cold taps. Ensuring water is stored at below the level in which legionella bacteria can grow, ensures the system is kept safe and reduces the risk of legionnaires’ disease. At temperatures below 20°, c legionella bacteria will lie dormant.

How to check water temperatures for legionella control?

In non-circulating systems the temperature must be taken at the sentinel outlets monthly which are those nearest and furthest from the calorifier and also at long pipe runs to ensure temperatures are above 50°c.

In addition to the above for circulating systems the temperature at the return pipework needs to be recorded to ensure the entire system is achieving 50°c minimum. 

Temperatures also need to be recorded on subordinate loops on a quarterly basis, it is important to check subordinate loops as there can often be an issue on a long leg, where it takes more than a minute for temperatures to rise, therefore providing a potential legionella risk.

A legionella risk assessment will set out the location where temperatures checks need to take place and will ensure high-risk areas are monitored for example where there are high-risk users.

Where can temperature issues occur within a hot and cold water system?

There are specific areas within hot and cold water systems were temperature can be a risk and allow legionella bacteria can grow. These include the bottom of calorifiers/water storage vessels where the incoming cold water enters and mixes with the stored hot water reducing the temperature of the water at the bottom of the vessel where debris and sediment collect. A shunt pump can be installed to reduce the risk of stratification and uneven temperature within the calorfier.

Dead legs in pipework, little used outlets can also provide favourable temperature conditions for legionella bacteria as the stagnated water temperature can rise to above 20°C.  Regular weekly flushing of little used outlets can reduce the risk of legionella bacteria growing in the system.

If the incoming mains temperature is above 20°c or there are areas within the cold water system which are exposed to heat gain this can also lead to the right conditions for legionella bacteria to grow.  Insulating pipework to reduce the risk of thermal gain will reduce the risk of the water temperature increasing.

What temperatures checks are needed on cold water storage tanks

The incoming mains and the stored water in the tank need to be measured to make sure they are both less than 20°C.  Every 6 months the temperature must be taken at the ball-valve and a record kept of the results.  It is good practice to carry this out both in summer and winter to ensure the stored water remains within the guidelines even when the ambient temperature is higher in summer months.  The average groundwater temperature in the UK is 12°c however during particularly warm summers the mains water can be above the desired 20°c, if this were to occur then the risk assessment would need to be reviewed and control measures put in place as appropriate.

Cold water storage tanks must be well insulated to protect the stored water from changes in the ambient air temperature.

The sentinel (nearest and furthest) cold water outlets for example taps and showers need to be checked on a monthly basis to check they are less than 20°c after running the outlet for 2 minutes.  It is also important to check a representative sample of taps on a rotational basis this helps to make sure the supply of cold water remains at a temperature that will not support the growth of legionella bacteria. A monitoring contract will establish the schedule of representative taps to ensure the entire system will be checked over a specified period of time.

What sort of thermometers are used for legionella monitoring?

Surface probe thermometers are used to record the temperature of water within pipework and a submersible probe used for recording the temperature of running water from outlets.

How do TMV’s affect temperature monitoring for legionella control?

Thermostatic mixer valves blend hot and cold water to produce water at the outlet which avoids the risk of scalding this is usually between 38°c and 46°c.  It is important to ensure the pipework downstream of the TMV is as short as possible to reduce the legionella risk.  A surface probe thermometer must be used to ensure the temperature of the hot water is at least 50°c prior to the TMV.

For recording temperatures can I use a paper based or electronic logbook?

It is vital to keep good records of all temperature monitoring.  It will identify where and if there are any issues and also an indication of trends.  A paper based logbook is adequate however we encourage customers to adopt our cloud based electronic log book as there is immediate reporting functionality to allow smart decisions and prompt actions to be taken.  The electronic log book is available for free to all our contract customers. Click the following link for more information on monitoring contracts

Can temperature monitoring for legionella control be carried out in-house?

Yes, however, the person taking the temperatures must be trained and competent to carry out the tasks and must understand the importance and significance of the findings.  Correct records must be held to allow trends and patterns to be assessed if necessary.  Dantek offer site specific training to allow individuals to carry out temperature monitoring. This practical site specific training in legionella control can help customers to reduce costs while also ensuring the legionella risk is controlled. 

For more information

Emma Reed

Employee profile: Emma Reed

When did you start working at Dantek?

I have been working at Dantek for 8 years, providing administrative support to the operations team.  I am responsible for producing certificates which are sent to customers for tank cleaning and disinfection work and reporting sample results to customers. 

I log all the samples taken by our engineers out on site and record them accurately including the customer, site, date, time, sample location (outlet) and sample type.  We take about 500 samples per month and each one must be carefully recorded onto a spreadsheet and submitted to the lab.

What type of samples do you deal with daily?

The most common samples I process are for Legionella, TVC (Total viable count), TVCC (total viable count and coliforms/e.coli), TVCC and pseudomonas aeruginosa taken for swimming pools.  LTHW closed system samples include TVC, NRB, SRB and Pseudomonas species.  Pseudomonas aeruginosa are often taken in health care premises.

All our samples are submitted to a UKAS accredited lab to be tested.  The lab emails me the results and I then take the necessary actions. This will include informing the account manager so they can decide on the next step including informing the customer of the results, I do this immediately when the results are positive.  With a Legionella sample, if serogroup 1 is detected this is the most serious and action will be required immediately. 

TVC are an indication of the total number of culturable bacteria in a given sample, with these we are looking at trends to indicate the bacterial activity in the water for example in a cooling tower. If any E. coli or coliforms are detected these are classed as a fail. 

When a sample has failed, we may advise a resample or where there have been multiple failures a disinfection is often required. It is important to consider past sample results and the level of detection in the sample.  In some instances, disinfection will not get the desired results so we may recommend that a chlorine dioxide system be installed.

What is a common question you often get asked by customers?

The most common question is how long will it take to get my results back?

12 days for final legionella results.  The lab inform us if there are any positive results on day 6 but these are interim results and could change. 

TVC results come back after approx. 5 days.  The lab will inform us if E.coli or coliforms are detected within 3 days.

SRB results take 21 days.  However we are able to supply the results for the other tests carried out alongside these (TVC, NRB, and Pseudomonas species) usually within 7 days.

Are there any factors which influence the samples?

Old buildings with old pipework and disused outlets can cause problems and increase the likelihood of getting a positive result.  Environmental factors like temperature can cause more bacteria to grow within systems so I did notice a spike in positive samples last summer for example.

It is very important to take the sample correctly and keep taps clean.  Little used outlets must be run weekly to prevent stagnation. Occasionally we can have issues with the way in which the sample was taken so following best practice is obviously the correct way to sample.  Our engineers are trained how to use aseptic techniques and follow specific procedures.

What do you enjoy most about your job?

I really like the people I work with and I am interested in the technical element of my work.  I am looking to improve my technical knowledge so I can advise customers and improve the service we offer. 

Legionella Sample Testing

Legionella testing – when do you need to take legionella samples?

Legionella sampling
UKAS accredited Legionella sampling

Do I need to take Legionella samples? 

It is a common misconception that taking Legionella samples is a requirement for Legionella control in domestic hot and cold water systems.  In fact, microbiological monitoring of domestic hot and cold water is not normally a requirement for compliance with current guidance. However, Legionella sampling would be required in high risk situations or in systems where current controls are shown to be failing. For example, if temperature control is consistently unachievable or disinfection concentrations are not satisfactory then alternative precautions should be carried out such as weekly microbiological sampling.

In high risk properties such as hospitals and health care premises, taking samples is a requirement. For specific guidance on microbiological monitoring refer to the BS 7592:2008 – Sampling for Legionella Bacteria in Water Systems – code of practice. 

It is very important to know that taking Legionella tests from domestic water systems does not achieve compliance with the HSE guidance document The Control of Legionella Bacteria in Water Systems ACoP L8.  The first step to compliance is to carry out a Legionella risk assessment and, then, to put in place a control scheme based on the findings of the risk assessment.

Whilst the ACoPL8 guidance are not law, they are enforceable under the Health and Safety at Work Act 1974 and the Control of Substances Hazardous to Health (COSHH) regulations. A Legionella risk assessment will define actions required for compliance with the guidance, and provide a schedule for any required ongoing monitoring e.g. temperature and biological monitoring if required.   

How long does it take to get a legionella sample result?

The most common question about legionella samples is how long will the results take?  Legionella tests must be analysed at an independent UKAS accredited laboratory. The incubation time for a Legionella test, using the standard culture method, is 10 days, so this is not a quick test to carry out. In the event of a Legionella positive result, the customer will be informed immediately by phone or email with advice about what to do next.

Different methods are available for Legionella testing which reduce the time to get a result from the lab. Some methods can produce a result in as little as 24hours. Please contact the Dantek office for further information if a fast turnaround is required. 

Where do samples need to be taken?

For sites where Legionella monitoring is a requirement in hot and cold water systems, sampling should be carried out in accordance with: BS 7592 Sampling for Legionella Bacteria in Water Systems. Depending on the complexity of the system, the actual number of samples will be worked out. It is important to ensure the sample is representative of the water flowing around the system and not just of the area downstream of the fitting; samples should be taken from separate hot and cold outlets rather than through mixer taps or outlets downstream of TMVs or showers. This will help to identify where any potential colonisation is and will help to inform on appropriate actions going forward.

A sampling plan should be put in place detailing the sampling locations and the type of sampling to undertaken. Whenever possible, samples should be taken from locations considered most likely to contain the highest numbers of legionellae.

Locations for Legionella samples in cold water systems

  1. From the point of entry of the mains or nearest outlet to the point of entry into the building
  2. Cold water storage tanks
  3. From nearest & furthest outlets (Sentinel points) on each branch of the system

Locations for taking Legionella samples in hot water systems

  1. From the nearest outlet to the calorifier
  2. From the base of the calorifier
  3. From the nearest & furthest outlets (sentinel points) on each branch of the system for single pipe systems
  4. From nearest & furthest outlets (sentinel points) on each loop of a circulating system

How is a legionella sample taken?

The scope and type of sampling (pre or post flush) should be set out in the sampling plan. Methods for the different types of sampling are detailed below.  If not specified pre-flush samples will be taken as standard.

A sample will be collected in a new, unused, capped, sterile litre sample bottle using aseptic techniques.  This minimises the chance of cross contamination of the sample and reduces the risk of a resample being required.  The bottles need to be labelled with the exact location where the sample was taken and the exact time and date. 

Dantek Technicians are trained to take the sample using aseptic techniques to prevent cross-contamination.  It is important that the correct sampling technique is used to achieve the most accurate results so that correct preventative actions are completed.

What is an aseptic technique for Legionella sampling?

Aseptic sampling techniques reduce the likelihood of contamination and poor sample results.

When taking samples, the technician must observe the following best practice:

  • Never touch the neck of the bottle or the inside of the lid
  • Ensure the bottle does not come into contact anything which may introduce contamination
  • Do not rinse the bottle out prior to the sample being taken
  • Minimise the time that the bottle is open to atmosphere
  • Only use the correct sterile bottle containing sodium thiosulphate or appropriate neutraliser.
  • Wash hands when sampling
  • Use hand sanitiser when sampling
  • Samples must reach the lab within 48 hours
  • Correct transport procedures should be followed
  • Ensure an air gap is left in the sample bottle

When taking a sample from a cold-water storage tank, the samples are to be taken from the centre of the tank where possible, taking care not to collect any solids.  Move the bottle forward through the water during sampling, ensuring water is only collected from in front of the bottle.

Steps to taking a Legionella sample:

  • Legionella samples must be taken in 1 litre sterile sample bottles containing sodium thiosulphate capable of neutralising up to 5ppm of free chlorine without effecting the bacteriological population.
  • Samples bottles, which are checked to ensure they are in date.
  • Samples bottles are checked before use to ensure that the lid seal is still intact.

Prior to removing the lid, the bottle should be marked with a permanent pen detailing the following information;

  • Customer
  • Site
  • Location of sample, building name, room location, cold water storage tank, calorifier, cooling tower sump, spa pool etc.
  • System identification, mains cold water, tank feed cold, domestic hot.
  • Pre or post-flush
  • Date & time of sample
  • Temperature of the water and/or chlorine dioxide reserve

How to take a pre-flush sample?

  • Do not disinfect the tap/outlet
  • Collect the sample immediately after the tap, or fitting, is opened, ensuring that the sample consists of only the first water which leaves the outlet.
  • Continue to fill the bottle leaving a 1 cm air gap at the top of the bottle.
  • Immediately replace the cap and invert the bottle several times.
  • Place the sample in a cool box and return to the office the same day.

How to take a post-flush sample?

  • Flush approximately 1 litre of water from the outlet.
  • Remove spray any inserts and flow directors from the outlet. It may also be necessary to remove and strainers and non return valves from TMV’s, strainers and solenoid valves.
  • Whilst wearing protective googles & gloves, make up a 200ppm solution of chlorine.
  • Clean the outside of the tap using the disinfectant solution.
  • Inject disinfectant solution into the outlet until it begins to run out of the tap using a wash bottle.
  • Descale and disinfect inserts and flow directors
  • Allow a two-minute contact time for the disinfection to take place.
  • Flush the outlet for 1 minute to remove the disinfectant.
  • Fill the sample bottle without adjusting the flow of water leaving a 1 cm air gap at the top of the bottle.
  • Immediately replace the cap and invert the bottle several times.
  • Place the sample in a cool box and return to the office the same day.
  • Rinse the outlet and surrounding area to remove any remaining disinfectant.

What should I do if the legionella sample comes back positive?

Firstly, don’t panic get in touch with Dantek and we will be able to guide you through the next steps to ensure you deal with the results in the correct way and to ensure your system is back under control as quickly as possible.  What action to take depends largely on the results and if this is the first positive result for the system.

If the first positive Legionella result is less than 1000cfu/ml:

If the minority of sample results are positive but less than 1000cfu/ml then arrange for a re-sample as soon as possible and review the control measures and risk assessment.

If the majority of the samples are positive but again with less than 1000cfu/ml then there is the possibility the system could be colonised at a low level.  Immediate review of control measures and risk assessment are needed and disinfection of the system must be considered.

If the 1st positive Legionella result is greater than 1000cfu/ml take the following action:

  • Arrange for a re-sample to be taken as soon as possible
  • Shut down any processes on the system where the positive sample was taken that can generate and disseminate airborne water droplets
  • Disinfect the system
  • Keep them shut down until sampling procedures and any remedial cleaning or other work has been done
  • Retest a few days after the disinfection and at frequent intervals afterwards until a satisfactory level of control is regained.
  • Review the risk assessment and control measures.

Following positive Legionella results a review of the Legionella risk assessment, control regime and record keeping/log books should be reviewed by checking the following:

  • They are current, up to date and accurate
  • That any remedial actions/recommendations have been completed
  • That the recommended control regime is in place. Identify the failing areas if there are any.
  • That good records are being kept of the activities undertaken
  • A record of the audit including any changes is placed in the log book

The question of whether to take samples or not can seem daunting however the key point to remember is taking samples will not affect levels of contamination on its own and does not necessarily offer compliance with the ACoPL8.  Ensure you keep your legionella risk assessment and control scheme up to date and seek advice from your water hygiene contractor.  If you have any concerns about Legionella samples, do get in touch with us as we are best placed to advice you about the Legionella control on your site.

Further reading:

BS 7592:2008 Sampling for Legionella bacteria in water systems – code of practice

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