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Legionella Risk in Water Tanks

Today we talk about water tank cleaning and disinfection


Over time cold water tanks, often found in lofts, basements and airing cupboards become dirty with debris, sediment, scale, sludge, biofilm, fouling, wall mold, stagnation, rust & corrosion, foreign bodies and plant growth. Should contaminants enter our water tanks or build up over time, they provide a breeding ground for bacteria such as Legionella bacteria and E.coli.

An annual inspection of cold water storage tanks will determine if cleaning and/or disinfection is required, as stated in the ACoP L8 (HSG 274 Part 2). Annual water tank cleaning is not a legal requirement, but annual water tank inspections are, where the water tank is inspected for its condition internally and externally. The water tank inspection will identify if a water tank clean is required or not.

Why do I need to clean my water tank?


Water tank cleaning is an essential part of water hygiene and Legionella control measures and something to be taken seriously both domestically and commercially. To maintain high quality water it is important that tanks are inspected regularly and cleaned when required to prevent bacterial proliferation. Protecting the water system’s users from potentially fatal diseases such as Legionnaires’ disease is vital, particularly when the users are vulnerable people such as children, the elderly, people with pre-existing illnesses, smokers, etc. These tanks should be inspected annually for their condition to identify if a water tank clean is required.

What else must I do with my tank?


Not only is it important to check your tanks for their internal conditions but they must meet design regulations as well, which help prevent bacterial growth inside the tanks. A poorly designed tank, clean or unclean may provide the right conditions for bacteria growth. For example, if your tank does not have a closely fitted lid, insects and bacteria may enter your tank. This is why tank design is just as important as a clean tank.

In summary, you must clean your tank where required, ensure it meets design regulations, and monitor your tank six monthly for its condition, design and temperature. Bacteria sampling is recommended on a six monthly basis to interpret the tank’s water quality. Legionella bacteria can double every 15 minutes.

About the tank clean.

Legionella and Fire Safe’s water treatment, tank cleaning and disinfection services are carried out by our fully trained engineers, provided with RAMS, method statements and procedures to ensure the work complies with the ACoP L8 (HSG 274) and COSHH regulations. Disinfection works are carried out with the use of chlorine with all RAMS designed to ensure the safety of the water system’s users is paramount.

When do I need a chlorination?


Where necessary, hot and cold water services should be cleaned, flushed and disinfected in the following instances, as specified in BS 8558:2011:

  • New water system installations or refurbishment of hot and cold water systems
  • Installation of new components
  • Systems that have been out of use for long periods of time
  • Evidence of contamination or stagnation in tanks
  • Substantial alterations to the systems
  • Following sample results indicating contamination
  • During or following an outbreak of legionella
  • Where indicated by the risk assessment


If you are uncertain on the actions you need to take then contact our team today.

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