Regular inspection and cleaning of domestic water tanks are important to keep water safe to use. Clean tanks also help meet HSG274 and ACoP L8 guidelines.
In this blog, we’ll explain why cold water tank cleaning matters and provide a straightforward step-by-step guide to getting it done right.
Why is Water Tank Cleaning Important?
Cleaning the water tanks is important for maintaining water hygiene and reducing the risk of Legionella. Over time, dirt, debris, mould, and bacteria in water like Legionella can build up in tanks. Regular cleaning and cold tank disinfection, guided by a proper Legionella risk assessment, helps remove these contaminants and keeps water systems safe and compliant with health standards.
When Should a Tank be Cleaned?
How often cold water tanks need cleaning depends on their use – whether they supply drinking water (e.g., for handwashing or consumption) or non-drinking water (e.g., for flushing toilets or rainwater storage). Drinking water tanks require more frequent maintenance as they supply water people consume.
According to the Health and Safety Executive’s HSG274 guidelines and ACOP L8 code of practice:
- Check the tank’s inlet and outlet temperatures at least once a year.
- Inspect the inside of drinking water tanks for contamination or debris every 6 months, and every 12 months for non-drinking water tanks.
- Test drinking water tanks for bacteria every 6 months. For non-drinking water, test when needed based on your control plan.
- Clean and disinfect drinking water tanks annually or when inspections show it’s needed. Non-drinking water tanks should also be cleaned when inspections identify a problem.
Even non-drinking water tanks need a risk assessment if there’s a chance of creating aerosols during use or maintenance (e.g., fire tank testing). Following these guidelines will help keep your water system safe and hygienic.
4 Steps to Clean a Cold Water Tank
Step 1 – Prepare
- Cleaning must be done by trained and competent people using the right equipment.
- Complete a risk assessment before starting work.
- Inform all building users that cleaning is about to happen (use signs if needed).
- Take photos of the water tank’s condition before starting.
- Isolate the tank inlet in two places if possible, so it can be drained.
- Isolate any booster pumps connected to the system tank following the manufacturer’s instructions.
Step 2 – Drain the tank
- Empty the tank into the agreed location, ideally an identified foul drain.
- Take a photo of the empty tank for the Log Book.
- If the tank needs to be entered, two technicians may be required if confined space safety rules apply.
Step 3 – Clean the tank
Manual cleaning involves:
- Scraping all internal surfaces.
- Vacuuming floors and walls with a wet vac.
- Removing visible scale, dirt, and debris.
- Sponging surfaces with a 14-15% liquid chlorine solution mixed with hot water.
- Disinfecting with chlorinated water to the required concentration (mg/l or ppm) of free residual chlorine.
- Once the chlorine level is correct and stable, open the tank outlet to circulate chlorinated water through the system.
- Chlorinated water must reach all outlets. A technician should check this by opening and flushing taps and showers one by one.
- Ensure 50ppm is achieved at all sentinel points for 60 minutes, or as specified in the method statement.
Step 4 – Recommission and Refill the Tank
- Once the contact time (or ‘kill time’) has passed, flush thoroughly with fresh water.
- Any chlorinated water being put to drain must be neutralised using a product scubas sodium thiosulphate.
- Flush the entire system until the free chlorine level at each outlet matches that of the incoming mains water.
- Refill the tank and restart the booster or circulating pumps following the manufacturer’s instructions.
- Take a photo of the water condition for the logbook.
- Once you have clean water, complete a disinfection label for each tank, updating the old sticker or covering it with the new one.
ACOP L8 & HSG274: Your Legal Duties and Obligations
Five Basic Principles of ACoP L8
- Identify and assess risks.
- Create a written plan to control them.
- Put precautions in place, manage them, and keep an eye on things.
- Keep records of what’s been done.
- Assign someone responsible for overseeing it all.
The Legal Framework
The Health and Safety at Work Act 1974 (HSWA), Control of Substances Hazardous to Health Regulations 1999 (COSHH), and Management of Health and Safety at Work Regulations 2002 (MHSWR) set clear rules to manage risks related to Legionella. These laws require employers and duty holders to assess risks, put controls in place, and monitor regularly to prevent exposure to harmful bacteria.
3 Common Cold Water Tank Contamination Risks
1. Stagnation and Bacteria Risks
Still water in low-circulation systems can encourage harmful bacteria to grow. This often happens due to low water usage, oversized tanks, blockages, or poor flow. Some stagnation is inevitable in water tanks, even in good conditions. Regular tank cleaning and disinfection help keep water safe and maintain quality.
2. Biofilm and Contamination
Cold water storage tanks can create the perfect conditions for biofilm and bacteria, including Legionella, to grow. Over time, rust, sediment, and silt build up in the tank. Without regular maintenance, contaminants can cause problems, and in some cases, organic matter like leaves or small animals can get into the tank, lowering water quality.
3. Debris from the Mains
Debris can enter the tank from the mains water supply and settle, creating conditions for bacteria and nutrients to grow. Regular checks and cleaning help stop tanks from becoming sources of contamination.
Professional Assistance: Why Hiring Experts Matters?
If cleaning a water tank feels like too much to handle or you don’t have the right tools and training, it’s best to call in a professional. We know how to clean tanks properly, follow safety rules, and meet legal standards like HSG274 and ACoP L8. We can also do risk assessments, handle any issues, and provide the necessary paperwork. Hiring experts like Comfort Services Group saves time, ensures the job is done right, and keeps your water safe.
FAQs
What happens if water tank is not cleaned?
If a water tank isn’t cleaned, it can become a breeding ground for bacteria, algae, and other pathogens. Sediment and debris build-up can contaminate the water, increasing the risk of health issues like Legionnaires’ disease from Legionella bacteria. Dirty tanks can also cause bad smells, discoloured water, and blockages in the system. Over time, neglecting cleaning can shorten the tank’s lifespan due to corrosion or damage from biofilm and sediments. Regular cleaning is key to keeping water safe and the system working properly.
Under what circumstances should a non-drinking water tank be cleaned?
Non-drinking water tanks should be cleaned if inspections show dirt, debris, or biofilm. Cleaning is also needed if aerosols might form during use, like in fire tank testing. Tanks with low water use or stagnant water should be cleaned regularly to stop bacteria from growing.
Why is it important to complete a risk assessment before cleaning a water tank?
A risk assessment helps find dangers like bacteria, chemical exposure, or confined spaces. It ensures safety steps are followed, like using the right equipment and methods. This protects workers, ensures proper cleaning, and meets legal requirements.
Can I clean the tank myself or should I hire a professional?
You can clean a tank yourself, but hiring a professional is safer and more effective. They have the right tools and training to clean tanks properly and follow the rules. Professionals also handle risk checks and provide records. Without experience, you might miss something important. It’s best to let experts handle it.
We are proud to share our experience and knowledge and take pride in offering this to all clients when required. If I, or one of the team can help then please schedule a meeting via the office or get in touch via one of our social media platforms.
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