Step 1: Preparation
Before you start the cleaning process, follow the steps below.
- Ensure the team cleaning the water tank(s) are suitably trained, certified and have the correct PPE equipment.
- Check the Risk Assessment prior to work to familiarise technicians and Responsible Persons with hazards associated with the task, asset(s) and how to reduce or control any risks identified.
- Inform / communicate with all building users that cleaning work is about to take place (use signs as appropriate to reduce or prevent usage of showers / taps during work).
- Photograph the condition of the water tank before commencing work.
- A pre-disinfection cleaning flush is required.
- The tank inlet must be isolated so that the tank can be drained and inspected.
- Any booster pumps associated with the system / tank should also be isolated from mains power supply.
Step 2: Emptying The Tank
- Empty the tank (to drain or as per the waste disposal licence as applicable).
- Take a photo of the empty tank for the Log Book.
- If entry is necessary, then two technicians must be present and confined space safety rules, regulations and procedures must be followed.
Step 3: Cleaning The Tank
- Manually scrape clean all internal surfaces and vacuum the floors and walls with a wet vac. All visible dirt and debris should be removed. Any signs of damage, corrosion, scale, flaking, black spotting, and deficiencies (e.g. missing rodent screens, cross flow vents etc) should be noted.
Step 4: Refilling The Tank
- Refill and flush the tank with fresh mains water checking for leaks during the refill process.
Step 5: Disinfection And Chlorination
- Note the pH of the mains water.
- For chemical disinfection, chlorinate the water in the tank to the specified concentration in mg/litre (ppm) of free residual chlorine.
- Determine the tank volume, required concentration, minimum contact time and dose per m3 in water.
- Use a chlorine test kit to check the Sodium Hypochlorite and do not add chemicals to the tank until the tank is half-filled with water.
- Add further Sodium Hypochlorite if required and re-test to achieve 50PPM free residual chlorine in the tank. Chlorine may be added at 0.5 litres per m3 and mixed in the tank. The concentration of free chlorine is affected by pH. Do not use it in systems with a pH greater than 8.5 and adjust the contact time according to the approved Method Statement.
- Once the required level of chlorine is achieved and maintained, the outlet of the tank may be opened to allow chlorinated water to flow around the system
- Chlorinated water flows to all outlets and needs to be checked by a technician by successively opening taps and showers. Use the most up to date Legionella Risk Assessment (or Water Hygiene Risk Assessment) to identify all sentinels (furthest points) and remaining outlets.
- Where testing all taps / showers is not possible or practical, as a minimum, test the sentinels at the end of each pipe-run along with a proportionate number of outlets along each leg.
- Ensure that 50PPM is achieved at all sentinels for 60 minutes or at least 20PPM for 120 minutes.
- If you believe the water tank will run dry whilst pulling water through the system, turn off the outlet valve to prevent air from entering the system and refill the tank half-way before adding in another dose of chemical and completing the fill of the tank.
- If disinfecting hot down services, allow water from the tank to flow to the calorifier.