It’s one of the most common questions facilities managers and landlords ask about their cold water storage tanks: how often should it be cleaned? The honest answer is that there’s no single fixed interval that applies to every building. Instead, UK guidance is built around regular inspection, with cleaning and disinfection carried out whenever an inspection shows it’s needed. Here’s how that works in practice.
What the Guidance Says
The Health and Safety Executive’s Approved Code of Practice L8 and its technical guidance HSG274 Part 2 set out how to control Legionella risk in hot and cold water systems. For cold water storage tanks, HSG274 recommends an inspection at least once a year, checking the condition of the tank and the temperature of the stored water. If that inspection finds sediment, debris, biofilm, corrosion or other contamination, the tank should be cleaned and disinfected.
Your building’s own Legionella risk assessment may call for more frequent checks, for example where the building is occupied by vulnerable people, the tank is in a warm location, or water turnover is low. For more on the wider rules, see our guide to cold water storage tank regulations.
When a Tank Should Be Cleaned and Disinfected
As well as acting on the results of an inspection, a tank should normally be cleaned and disinfected:
- When an inspection finds sediment, debris, slime or dead insects in the water
- When the tank has been contaminated, for example by a damaged lid or unscreened vents
- After repairs or alterations to the tank or the pipework it serves
- When a new tank is installed, before it goes into service
- When a building or part of a system has been out of use for a long period
- When there are complaints about the taste, smell or colour of the water
- When water sampling or your risk assessment shows a problem
Signs Your Tank Is Overdue
If you can safely look inside your tank, these are the warning signs that it needs attention now rather than at the next inspection:
- A layer of sediment or rust on the floor of the tank
- Slime or biofilm on the walls or at the waterline
- Insects, debris or anything floating in the water
- A lid that is missing, damaged or doesn’t fit properly
- Stored water above 20°C
What a Professional Tank Clean Involves
A typical commercial tank clean starts with a survey and a quotation with a risk assessment and method statement. Where the building needs water throughout, a mains bypass or temporary tank is set up. The tank is then drained, sediment and debris are removed, the internal surfaces are cleaned, and the tank and pipework are chlorinated before being flushed, refilled and returned to service. Find out more about our water tank cleaning and servicing.
Cleaning Only Works If the Cause Is Fixed
If the same tank keeps needing cleaning, there’s usually an underlying reason: a poorly fitting lid, missing insect screens, poor insulation that lets the water warm up, or a tank that’s too big for the building so water sits for too long. Putting those right, through remedial work, refurbishment and relining or, for tanks at the end of their life, cold water storage tank replacement, is the best way to keep stored water clean between inspections.
If an inspection has flagged compliance issues, our Legionella and L8 compliance upgrades service can help.
Frequently Asked Questions
Is there a legal requirement to clean a water tank every year?
There’s no fixed legal cleaning interval. The legal duty is to assess and control the risk from Legionella. HSG274 recommends inspecting cold water storage tanks at least annually and cleaning and disinfecting them when the inspection shows it’s needed.
Who is responsible for making sure a tank is inspected?
The employer or the person in control of the premises, such as a landlord, managing agent or facilities manager, is responsible for making sure the risk assessment is in place and control measures, including tank inspections, are carried out and recorded.
Can the building keep its water supply while the tank is cleaned?
Usually, yes. Where needed we set up a mains bypass or temporary tank so the building stays supplied while the work is carried out.
Need Your Tank Cleaned?
Express Water Tanks is a family-run business with over 25 years’ experience in the cleaning, repair, refurbishment and replacement of commercial water tanks. Our engineers are available 24 hours a day, 365 days a year. Call 01206 239804 or get in touch online.
This guide is a general overview and isn’t a substitute for a site-specific risk assessment or advice from a competent person.
