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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.

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

Water Tank Cleaning and disinfection

Legionella control for social housing


MCCH support around 2000 people across London and the South East who have learning disabilities, autism or mental health issues.

Dantek have worked for MCCH since 2006 providing legionella prevention and control solutions.

Recently we carried out a tank cleaning contract at 17 sites across their portfolio.

The tanks were identified in the legionella risk assessments as requiring cleaning.

Our experienced Engineers and Operations staff worked with MCCH to organise access and liaise with service users to schedule appropriate times for the work to take place.

London Academy tank replacement, tank renewal and plumbing alterations

Water tank cleaning
Harry works hard to clean 3 tanks of all sediment and debris

water tank installation
Working as a team to install the new cold water storage tank

3 of our Engineers worked exceptionally hard to complete a complex tank renewal and tank replacement job at an Academy in London. They carried out plumbing alterations and replaced 2 x 40 year old 20 tonne tanks. This job required expert planning and skill to successfully ensure it was completed on time and to our high standard, ensuring compliance with current guidance for legionella control.

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