Cold water tank inspections and remedials: what we look for

Cold water storage tanks are out of sight and out of mind for most people. They sit in lofts, plant rooms and cupboards for decades, quietly collecting dust, dead insects and the odd surprise. Here's what happens when we inspect one, what we usually find and what can be done about it.

March is a good time to get tanks looked at. The weather's starting to warm up, lofts and roof spaces will be getting hotter over the coming months, and it's much nicer to deal with a tank problem in spring than in the middle of a heatwave.

Why tanks matter for Legionella

A cold water tank holds a volume of water that isn't moving all the time. If the tank is in a warm space, if it's bigger than the building needs, or if dirt has got in, you've got the ingredients Legionella likes: warmth, stagnation and nutrients.

Most tanks feed showers, taps and hot water cylinders, so anything growing in the tank can end up spread through the whole system. That's why the HSE's technical guidance, HSG274 Part 2, says tanks should be inspected at least once a year, with their temperatures checked regularly too.

What we look at during an inspection

1. Access and safety. Can the tank be reached safely? Loft hatches, boards and lighting all matter. Sometimes the first recommendation is simply to make it possible to inspect.
2. The lid. Is there one, does it fit properly and is it secured? A loose sheet of hardboard doesn't count.
3. Screens on the overflow and vent. These should have fine mesh to keep insects and debris out.
4. Insulation. Both the tank and the pipes connected to it, to protect against heat in summer and frost in winter.
5. Water temperature. We measure the water in the tank and compare it with the incoming mains. Cold water should be kept below 20°C.
6. Inside the tank. We look for sediment on the bottom, slime or biofilm on the walls, rust, scum on the surface and anything that's fallen in.
7. Size and turnover. A tank that's far bigger than the building uses means water sits for days before it's drawn off.
8. Condition of the tank itself. Cracks, bowing, corrosion, leaks and the state of the ball valve.

We photograph everything so you can see exactly what we saw, and you get a written report with any recommendations in order of priority.

The faults we find most often

• Missing or poorly fitting lids. Easily the most common. Without a proper lid, dust, insects and occasionally birds or rodents get in.
• No insect screens. Overflows and vents left open to the loft.
• Sediment and debris. A layer of silt or rust on the bottom, which gives bacteria shelter and something to feed on.
• Warm water. Usually because the tank's in a hot loft or plant room with poor insulation.
• Corroded galvanised tanks. Older steel tanks rust from the inside, which adds sediment and eventually leaks.
• Redundant tanks. A tank that no longer serves anything, or one left in place after the building went over to mains pressure.

The remedial options

What we recommend depends on what we find. Typical remedial works include:

• Fitting a proper lid and screens. Often a quick, cheap fix that makes a big difference. The Water Supply (Water Fittings) Regulations 1999 expect stored drinking water to be protected from contamination, which in practice means a rigid, close-fitting lid and screened openings.
• Cleaning and disinfection. The tank is drained, cleaned out and disinfected, then refilled and flushed through. It's done to a recognised procedure, and samples can be taken afterwards to confirm it's worked.
• Insulating. Better insulation on the tank and pipes helps keep summer heat out.
• Replacing the tank. If it's corroded, cracked or can't be cleaned properly, a new tank that meets the current regulations is often the better long-term answer.
• Downsizing. Replacing an oversized tank with one sized for actual demand improves turnover.
• Removing it altogether. In some buildings it's possible to feed outlets directly from the mains or a booster set, getting rid of stored water entirely. Whether that works depends on your mains pressure and flow, so it needs looking at case by case.

A typical scenario

Picture a 1930s house converted into three flats, with a single galvanised tank in the loft feeding all of them. The lid is a piece of plywood, the overflow has no screen and there's a layer of rust and silt on the bottom. In July the tank water would likely be well above 20°C.

In that case, a clean and disinfection would only buy time because the tank itself is deteriorating. A replacement plastic tank with a sealed lid, screened overflow and vent, and proper insulation would deal with the root causes. We'd also check the pipe runs through the loft while we were there, as long uninsulated runs in a hot roof space cause their own problems.

Between inspections

Once a tank's in good shape, keeping it that way is fairly simple. Keep the lid on and secured, check the temperature at the intervals your written scheme sets, and keep up the annual inspection. If you notice anything odd, such as a change in taste, colour or smell at the taps, get it looked at sooner.

If you're a landlord with a tank in the loft, it's one of the main things your risk assessment will focus on. Our guides on whether landlords need a risk assessment and HMO licensing and Legionella explain why.

We can carry out tank inspections as a one-off or as part of our Legionella maintenance visits, and quote for any work that's needed while we're there.