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Legionella control case study at a large boarding school

Dantek have provided legionella control services to Marlborough College for a number of years, below is a case study about how we work together to ensure ACoP L8 compliance and the safety of the students and staff.

Since its establishment in 1843 by a group of Church of England clergymen at the Castle Inn at Marlborough, Marlborough College has never been frightened of change. 

In its recent history, numerous academic initiatives have been fostered at the College including, Business Studies, SMP Maths, Combined Science, Pre-U examination syllabuses and the teaching of Arabic and Chinese. In 1968 Marlborough was one of the first of the traditional boys’ boarding schools to admit girls into the Sixth Form.

In 1989, the College became fully co-educational with the admission of girls into the Lower School and with the establishment of the first of the all-girl boarding houses.

Today the College caters for 936 pupils (of which just over 40% are girls) and the great majority of whom (98%) are boarders.  The remaining four “Out-College” houses accommodate 13-16-year-old boys, plus a mixed Sixth Form of both girls and boys.

School size: 201-500 employees

Based at: Marlborough, Wiltshire

The support Dantek provides

As a school, Marlborough College provides care for a large group of students most of which board on site, this means that they must adhere to strict health and safety guidelines. One of these areas is the need to protect students and staff from potential Legionella infection. Dantek has worked with the school for many years ensuring they comply with all regulations thus providing a safe environment for their students to thrive in.

As part of their on-going activity, Dantek engineers monitor the water quality, carry out remedial work and run regular testing and Legionella risk assessments. The College compliance team benefit from using Dantek’s electronic logbook which saves time and helps them keep on top of the various requirements. Dantek has provided a long-standing service to the college and act as part of their team which supports the quality of environment and interaction required by the College.

What does the client say?

We caught up with Kelvin Neale, M&E and Energy Manager at Marlborough College to find out how he views working with Dantek;

How did you hear of Dantek?

I have worked at Marlborough College for 8 months so Dantek were already in place when I joined. However, I did work with Dantek through another employer. I can certainly say that Dantek are known for their sound reputation in the industry.

What are the most important elements you look for in a contractor?

The most important elements for me are timely communication and a conscientious, effective manner. Due to the nature of the work Dantek provide, I also look for clear paperwork and accurate paper trial. We do consider the price, but it is not the only factor. When it comes to compliance, we must make sure we are choosing the right supplier who has the knowledge and systems which we require.

What do you like about working with Dantek?

I am very happy with their work in general. Three things stand up for me in particular:

  1. All engineers are professionals and knowledgeable, DBS checked and employed directly. They will always provide a service that goes beyond their contractual requirements and nothing we ask is ever an issue.
  2. The level of knowledge and expertise the company holds is impressive, they clearly know their stuff. I am also very impressed with the fact that on the rare occasion when they come across something they don’t know; they will go away to research for the right solution. It really demonstrates how competent they are and allows me to trust their advice implicitly.
  3. The electronic logbook is helpful and saves me a lot of time. It means I always have the data I need available to me and we never miss any tests and activities we need to complete.

How do they stand out against the competition?

As mentioned before, Dantek has a strong reputation in the industry. I think the main elements that make them stand out for me are as follows:

  1. The concise and timely completion of every job
  2. The electronic logbook which allows me to stay on top of compliance requirements, documentation and paperwork
  3. The level of knowledge and expertise they demonstrate about water treatment and legionella control


Clean Cold Water Storage Tank

Why is water tank cleaning important for legionella control?

Keeping water tanks clean is a fundamental part of a water hygiene regime. Here are three key reasons why.

  1. Removing any habitat for Legionella:  Legionella bacteria requires nutrients to grow, these can be found in tanks which over time can gather silt, scale and sediment which provide nutrients for bacteria such as legionella. Water storage tanks can become contaminated with organic matter like leaves or even small rodents if the correct screens are not fitted. Cold water storage tanks can too often be out of sight and out of mind.
  2. Water stagnation: stagnant water can provide the habitat in which legionella bacteria can grow.  Scale can trap nutrients and cause a biofilm which can act as a barrier to disinfectants.  By draining and physically cleaning a water tank any scale, sludge and biofilm is removed.
  3. Legal Compliance: There are legal obligations surrounding the inspection and if required cleaning and disinfecting of water tanks and maintaining records of the work carried out. These records allow you to prove you are taking the correct action to prevent legionnaires’ disease.

At Dantek our water tank cleaning and disinfection services are carried out by in-house, fully trained, professional water tank cleaners.

All water hygiene contracts with Dantek will include regular cold-water storage tank inspections with the information gathered (including photos) held in a cloud-based compliance logbook. The logbook is included free as part of all contracts, allowing you easy access to all information held about the condition of your cold-water storage tanks. Please get in touch to see how it could work for you.

Recently we carried out a clean and disinfection of a large cold water storage tank, below are photos of before and after the cleaning process.  It is clear in figure 1 there was a high level of sediment visible in the water tank which needed to be removed to reduce the risk of legionella bacteria.

Image of a cold water storage tank before it is cleaned and chlorinated.
Visible sediment in cold water storage tank prior to cleaning and disinfection.
Before and after photo of a large cold water storage tank being cleaned and disinfected.
Cold water storage tank after cleaning and disinfection.
Annual Cold Water Storage Tank Inspection

Top tips for inspection of cold water storage tanks

An annual inspection of cold water storage tanks is required to record the condition of the tank and the water within it.  It is also a requirement to check the temperature of stored water during the summer to ensure it remains below 20°C.

A trained Water Hygiene Technician must inspect the cold water storage tank and record the condition in the monitoring log book.  Any non-compliances are escalated in accordance with the chain of command stated in the control scheme and remedial actions carried out to ensure the tank remains in good condition within an appropriate timescale.

An inspection includes a check of both the inside and outside of the tank and the water held within it.  The lid should be tightly fitting and in good condition.  The insect and vermin screen on the overflow and warning pipes must be fitted and also in good condition.  The tank must be lagged which will help to maintain a constant temperature of the water and prevent it getting too warm or cold.  The surface of the water must not have a biofilm or show signs of stagnation.  The inlet and outlet of the tank should be opposing to also prevent stagnation.

Figure 1 below taken from page 26 of the HSG274 demonstrates the condition of cold water storage tanks and when action should be taken.  This traffic light system indicates actions to be taken and also the time frame in which they should be completed. 

Condition of cold water storage tanks and when action should be taken
Figure 1: HSG274 Legionnaires’ Disease p26

Regular tank inspection are an important part of a legionella control scheme because by preventing the habitat in which legionella bacteria can grow and proliferate you are ensuring the system will not provide the conditions suitable for harbouring legionella bacteria so therefore keeping your water system and ultimately your people safe.  

Checking Temperature On A Calorifier

5 key issues to consider about Legionella and care homes

Legionnaires’ disease can cause serious illness and, in some cases, even death if it is not managed correctly.  It is contracted by breathing in droplets of air containing Legionella bacteria.  Legionella bacteria occurs naturally and enters the water system through the mains water supply.  Airborne water droplets are created by water systems such as showers, spa baths, hydrotherapy baths and hot and cold-water services such as spray taps.

While anyone could become infected there are some groups who are more susceptible, and these include the elderly and those with existing underlying health conditions.  Therefore, it is so important for Care Homes to act and put in place a robust management system and practical solutions to protect anyone in their care who may be at risk from the disease.

There are no known cases of Legionnaires’ disease from the natural environment, this is because it is only in man-made water systems where the conditions are right for the bacteria to proliferate.

Earlier this year the private care provider BUPA was fined £3m for failing to prevent and control an outbreak of Legionnaires’ disease when very sadly a resident died. Click on the link below to read more:

Checking temperature on a calorifier
Checking temperature on a calorifier

Where to start?

Controlling legionella in nursing and residential care homes starts with a legionella risk assessment of the hot and cold-water systems to ensure a scheme is put in place to control the risk.  Temperature is the usual method of control with systems operated at the required temperatures to prevent legionella bacteria from growing.  Hot water must be stored at 60°c and distributed at 50°c or higher to all outlets.  Thermostatic mixer valves may need to be fitted at outlets to prevent scalding.  Cold water must be stored and distributed at 20°c.

Regular checks need to be carried out in accordance with the risk assessment, some of these checks can be carried out by your own trained site staff or alternatively you can choose an experienced water hygiene company to do these on your behalf.  Whichever option you choose a key factor for compliance is the management of the control scheme which includes correct record keeping.

Cold water storage tanks must be visually inspected at least every 6 months and cleaned as required. The temperature of stored water must be checked to ensure it is 20°c or less.  Showerheads and hoses must be cleaned and descaled quarterly.   Calorifiers (hot water cylinders) need to be drained and internally cleaned and inspected annually.

It is also important to reduce the possibility of stagnating water in a system, so a risk assessment will identify dead-legs in the pipework which will need to be removed.  Little used outlets which can include showers and taps must be flushed weekly or removed to prevent stagnation.

Electronic log book

Using a cloud-based log book is one of the best ways to keep on top of all the monitoring tasks which need to be performed.  Dantek has developed an easy to use cloud-based system which we provide for free to all our contract customers.  The system ensures all your data for legionella compliance is held in one place and can be reported on and scrutinised, so you know where any problems are and what you need to do to rectify them.  For a short demo of the system please email

5 key points to consider

  1. Do you have an up to date legionella risk assessment and control scheme in place?
  2. Who is the competent person to manage the risks from legionella?
  3. Are your water systems kept clean, with correct temperature controls and no stagnant water?
  4. Are you frequently checking temperatures remain in line with the ACoPL8 HSE guidance?
  5. Do you have accurate records in place to show external agencies?

Dantek is listed on the Legionella Control Association directory of companies who specialise in the prevention and control of legionella bacteria. Do get in touch if you would like to find out more about our legionella prevention and control plans.

Frequently asked questions about Legionella control

Legionella control FAQ’s

What is Legionnaires’ Disease?

Legionnaires’ disease is a potentially fatal pneumonia caused by inhaling legionella bacteria.  Infection is caused by breathing in small droplets of water contaminated by the bacteria in the lungs.

Legionellosis is the term used to describe the diseases caused by legionella bacteria, of which Legionnaires’ disease is potentially fatal.  Pontiac fever and Lochgolihead fever are the less serious conditions but none the less avoidable if the correct cause of actions is taken.


Who can catch Legionnaires’ disease?

Everyone is potentially susceptible to infection, but some people are at higher risk e.g. those over 45 years of age, smokers and heavy drinkers, those suffering from chronic respiratory or kidney disease, and people whose immune system is impaired.


Where is legionella found?

Legionella bacteria (legionella pneumophila) are common in natural water courses such as rivers and ponds.  Since legionella are widespread in the environment, they may contaminate and grow in man-made water systems such as cooling towers and hot and cold-water services.  Spa baths, Jacuzzi’s and hot tubs are also provide a potential breeding ground for legionella bacteria as they provide optimum conditions for the bacteria to grow and multiply to sufficient numbers for a system to be colonised.

The bacteria thrive at temperatures between 20 and 45 degrees, particularly if there is a supply of nutrients such as rust, sludge, scale, algae and other bacteria.

The risk of legionnaires’ disease is increased if water droplets are produced and dispersed in aerosol form for example in a shower or spa bath.

It is possible to reduce the risk by removing exposure to water droplets and aerosol and by removing the nutrients on which the legionella bacteria feed.  This can be done by keeping water systems clean by cleaning and disinfecting cold water storage tanks and showerheads.


How do I comply with latest HSE guidance?

The current HSE guidance documents for the legionella control are the L8 Approved Code of Practice and the HSG274 Legionella technical guidance.


The first thing to do is a Legionella Risk Assessment, to consider the risks from legionella that may affect your staff or members of the public, and then take suitable precautions to control and prevent the risk.



Is it a legal requirement to have a legionella risk assessment?


There is a legal duty for employers and landlords to consider the risk legionella bacteria in buildings under your control or management. You must identify and assess the source of risk i.e carry out a legionella risk assessment. Manage the risk. Put in place measures to control or prevent any risks.  Keep good records to prove you are taking the appropriate action and to show to external agencies you are following the HSE guidance for legionella control.


What can be used to control legionella bacteria?

Temperature is usually used in hot and cold-water systems, by keeping hot water at above 60 degrees and ensuring it is above 50 degrees at the outlets. Cold water should be kept at below 20°c.

There are other methods which can be used if temperature is not an option, such as copper/silver ionisation and chlorine dioxide.  Cooling towers / systems are often treated with biocides.  There are other treatment strategies available such as ultra violet (UV) irradiation.


Do I need to take Legionella samples?

This depends on the risk assessment and control methods being used.  In some circumstances it will be required, however it needs to be done at a UKAS accredited laboratory and will require specialist help.  Dantek can provide advice on sample frequency and locations, and what to do if Legionella is detected.


Routine Legionella testing however is not a requirement in domestic hot and cold-water systems.  It would only be recommended in hot and cold-water systems due to exceptional circumstances where typical control measures are not working.  A full legionella risk assessment would identify the best course of action to reduce the risk.


To get an indication about whether microbial control is being achieved taking a TVC sample (total viable count) will allow the system to be monitored.  TVC samples are normally carried out for cooling towers and spa pools.  For other systems the risk assessment will identify is sampling is recommended.


Where can I get more information?

  • Order a copy of the Approved Code of Practice and guidance Legionnaires’ Disease: The control of legionella bacteria in water systems L8 here »
  • Contact the Water Management Society (WMS)
  • Check out the LCA legionella control association directory of Water Hygiene companies
  • Call Dantek for free expert advice and support about all legionella control issues


What will a legionella risk assessment cost?

The cost will depend on what assets are on your site and how many buildings.  For large sites or multi-site portfolios a site visit by one of our team is the best way to establish exactly how much a risk assessment will cost. However, we are often able to provide a guide price if you know roughly the size and type of building.  For example, how many floors, what it is used for, whether there are any cold-water storage tanks, number of calorifiers and if there are any cooling towers. An asset register of plant and equipment can be very helpful in determining how long the on-site assessment will take and therefore the cost.


One of our team would be happy to talk through on the phone any requirements and enquiries.


What do Landlords need to do about Legionella control?

The law clearly states if you are a Landlord and rent out your property then you have a duty under Health and Safety Law to consider the risk posed by Legionella bacteria. The ACoP L8 (3rd edition) also states Landlords must assess the risk from exposure to legionella to their tenants.

In most cases the risk assessment is simple and straight forward, however for more complex systems or if the Landlord is not able / competent to carry out the assessment they can use a specialist Water Treatment Company like Dantek, to carry out the legionella risk assessments and advise on any actions required.

A simple risk assessment will identify if a system is considered a low legionella risk and no further actions are required other than to review the assessment regularly in case anything changes which may affect the risk for example the water system in the building changes.

Examples of low risk systems include;

  • A small building occupied by people not considered at risk from legionella bacteria.
  • Where there is enough usage of water per day to ensure the entire system is changed at least once.
  • Mains fed cold water supplies the entire system, so there are no cold-water storage tanks.
  • Hot water is fed from combi boilers/ instantaneous heaters or low volume water heater where the hot water is supplied at no less than 50°c
  • The only outlets at the property are toilets and wash hand basins with no showers present on site.


What is meant by the term water system?

A water system includes all plant and equipment for example all the pipework, pumps, cold water storage tanks, valves, showers, water softeners, chillers, heat exchangers, cooling towers, calorifiers, little used outlets and dead legs, humidifiers, air washes, car washes, indoor fountains and water features.


How do I choose a water hygiene company?

Choosing a water hygiene company with the knowledge and skills to manage and control the risk of legionnaires’ disease at your site is made easier with the help of the Legionella Control Association.  The LCA hold a register of members who have met their requirements on an annual basis and have passed their annual audit of systems.

A key factor should be the training of site staff to carry out water hygiene work competently.  A provider will be able to demonstrate how their employees are trained and audited to ensure continual compliance with current standards.

The LCA code of conduct sets out the standard of service a client should expect from a water hygiene provider.  The code requires a Service Provider to set up an appropriate management system for the control of legionella complying with the latest HSE guidance for the control of legionella bacteria.

How many cases of Legionnaires Disease were there last year?

The figures for 2017 are not available yet however in 2016 according to a report by Public Health England, there were 359 cases of Legionellosis cases reported to the National Surveillance Scheme for Legionnaires’ disease in England and Wales.  70.4% of these cases were male and 29.6% female.  With 60% of the cases were reported in people over the age of 60.

57% of cases are thought to have been infected by the organism in the community, with 41% of cases relating to travel abroad and 2% relating to healthcare premises.  Three quarters of those who were diagnosed already had an underlying health condition making them more susceptible to legionnaires’ disease.

The HSE take the view that all these deaths were preventable as it was a man-made system which allowed the bacteria to grow and proliferate to cause an outbreak.  As such the HSE take the view that all businesses should consider the risk from Legionella bacteria and follow the AcoPL8 and HSG274 guidance on the best way to prevent and control it.


Warm weather and Legionella risk?

Checking the temperature of stored water

The HSE recommend summertime to inspect cold water storage tank temperatures, to ensure the stored water is kept below the recommended 20°C throughout the year.  With high temperatures forecast for the next week, temperatures particularly in roof spaces can increase significantly.  Good fitting Insulation on cold water storage tanks, together with a regular through flow, should ensure the temperatures of the stored water is kept below 20°C, however further actions may be required if temperature control cannot be maintained.

In exceptionally hot weather like we are currently experiencing across the UK, mains water supplied can increase to a surface temperature of up to 23°C, clearly if this were to happen steps would need to be taken to ensure high turnover of stored water and the prevention of stagnation.

In an exceptionally hot summer it may be necessary to review the legionella risk assessment and make any appropriate changes to the control regime, to reduce the risk of legionella bacteria multiplying to sufficient numbers to potentially cause an outbreak of Legionnaires’ disease.

Our highly trained Water Hygiene engineers at Dantek can inspect your cold water storage tanks, and our Legionella Risk Assessors can offer advice about what to do if your system is not achieving adequate temperature control.

Please call now for a free consultation 01454 417920.

Water tank cleaning


Keeping your water tanks clean is an important part of a water hygiene regime. Sludge, scale and debris must be removed to ensure a habitat for legionella bacteria is not created.

Our team recently cleaned and disinfected a group of interconnected tanks which fed a hotel, the before and after photos below demonstrate the condition of the cold water storage tanks before and after the clean and disinfection work was carried out.

For this job our engineers used a disinfectant called  Sanosil.

SANOSIL is a stabilised aqueous solution of hydrogen peroxide containing colloidal silver and other stabilising materials.  COSHH data can be provided prior to work commencing. The product is WRAS approved and listed in the water fittings and materials directory for emergency disinfection of potable water systems.

Before cleaning and disinfection this tank was in a very poor condition

Cleaning a cold water tank

During the cleaning and disinfection process

Chlorination of tank

Tank ready to be refilled with clean water

Cleaning tanks


For an instant quote to carry our tank cleaning work at your site please call 01454 417920 today or email


When do potable water tanks need to be cleaned?

Potable water tank
When do you need to clean a drinking water tank?

Drinking water or potable water tanks must be kept in good condition, be correctly installed and designed to ensure the water quality is maintained, and is fit for human consumption.

If you rely on tank fed water for your drinking water, then it should meet the following requirements:

  • Correctly sized so stagnation does not occur, and fresh water is replenished frequently.
  • Constructed of a WRAS approved material e.g. plastic (polyethylene) and have a close-fitting lid.
  • Has a lid which excludes light and is tightly fitted and securely fastened to prevent birds, rodents and dust from getting into the tank.
  • Has a lid vent and overflow with a screen to prevent dust, insects, birds and vermin getting into the tank.
  • The tank must be insulated to keep temperature below 20 degrees.
  • Inspected visually at least annually to make sure there has not been a build up of scale or sludge and the lid and screens are all securely in place.
  • Cleaned and disinfected annually or sooner if microbiological monitoring indicates deterioration or if visual inspection shows sludge, scale or corrosion.
  • Microbiological samples should be taken at intervals of not more than 6 months if there is a change in water quality, the tank is not adequately protected, it leaks or is corroding.


Dantek can offer advice to correctly identify potable water tanks and then monitor those tanks to ensure the water quality remains fit for human consumption. For a free consultation about your cold-water storage tanks please call 01454 417920 today.

How often do cold water storage tanks need to be cleaned and disinfected?

Clean cold water storage tank

Cold water storage tanks should be kept clean and free from nutrients, including corrosion, scale and biofilm (HSG274 part 2). 

However there is in fact no definitive recommended timeframe for cleaning tanks, so they must be cleaned as necessary or if any of the following occur: 

  •  Installation of new water system or refurbishment of hot and cold-water system
  • Installation of new components to the water system 
  • When the hot and cold-water system has not been used for long periods and has not been flushed 
  • When routine inspection of the tanks deems it necessary because there is visible evidence of contamination or stagnation 
  • If the system has been significantly altered or entered for maintenance purposes 
  • If water samples taken from the system show there is evidence of microbial contamination 
  • During or following an outbreak of legionnaires’ disease associated with the system 
  • When a risk assessment has indicated a tank clean is necessary 


A chemical disinfection will typically be chlorine or hydrogen peroxide dosed to achieve the required ppm and maintained for at least an hour throughout the water system. The chemical is pulled through to all outlets and tested to ensure the entire system is treated effectively. 

After the disinfection and before the system is put back in use the disinfectant must be flushed from the system if using chlorine, or if using hydrogen peroxide be below the maximum level for potable water. 

Dantek have a team of highly trained technicians who carryout this type of work regularly. We are experienced in cleaning all sizes of tanks from small 50-gallon tanks in nursing homes to very large industrial size and everything in between. 

To get a quote for tank cleaning please contact our sales team who will be able to advise what to do at your site. 01454 417920

Legionella electronic log book in action

Tank cleaning
Cold water storage tank requires cleaning and disinfection


During routine monitoring of cold water storage tanks at a school a large amount of debris was recorded and photographed with the Dantek electronic monitoring log book.  The tank was cleaned and disinfected and then remarkably on the next tank inspection 6 months later the tank was dirty again.  The photos of the tank demonstrated there was clearly something unusual about the amount of debris, after further investigation the problem was found, and the solution was to add a filtration system to prevent debris and sludge entering the tank.

Being able to monitor and act on evidence has ensured the cold-water storage tanks remain clean and compliant with the ACoPL8 and the pupils and staff using the water at the school remain safe.

If you would to see the electronic log book please contact us as we are happy to come to your site and show you how it works.

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