The cold water storage tank is out of sight in an attic or plant room, and it is often where legionella problems begin. An assessor checks eight things about every tank. Most faults are cheap to put right once someone has looked.
1. Lid
The tank should have a rigid, close-fitting lid. An open or loosely covered tank collects dust, insulation fibres, insects and worse. All of it becomes food for bacteria.
2. Screens
Overflow and vent pipes should be fitted with screens so that insects and vermin cannot get in.
3. Insulation and location
Stored cold water should stay below 20°C. A tank in a hot roof space, beside a boiler or under uninsulated hot pipes will warm into the range where legionella grows. The assessor measures the water temperature and looks at what is heating it.
4. Sediment, scale and slime
Sediment on the base, scale on the walls and a slimy film at the waterline all shelter and feed bacteria. Their presence usually means the tank needs cleaning and disinfection.
5. Size and turnover
A tank should hold roughly a day’s supply. Many are far bigger than the building now needs, especially where occupancy has fallen. Oversized tanks hold water for days, and stored water warms up. The fix can be as simple as lowering the water level.
6. Flow through the tank
Where the inlet and outlet sit side by side, fresh water leaves straight away and the rest stagnates. Linked tanks can have the same problem if water passes through only one of them.
7. Condition and materials
Corrosion, damaged linings, old galvanised tanks and unsuitable jointing materials are noted, along with any leaks or signs of past overflow.
8. Access
If nobody can reach the tank safely, nobody inspects it. The assessor records whether there is safe access, lighting and enough room to lift the lid.
What happens when a tank fails the check
- Clean and disinfect: the tank is drained, cleaned, disinfected, flushed and returned to service, with a record of the work.
- Repair: a new lid, screens or insulation.
- Adjust: lower the stored volume or change the pipework so water flows through.
- Replace: where the tank is beyond repair.
How often to inspect
Your legionella risk assessment sets the interval. An annual inspection is common, with the temperature checked more often, particularly in summer. For more detail on the cleaning process, see cleaning and disinfection of water storage tanks.
Safer Solutions inspects, cleans and disinfects water storage tanks and carries out legionella risk assessments across Ireland. Call 086 275 9728, email info@safersolutions.ie or request a quote.