Where it comes from
London sits on a chalk and limestone aquifer. Water moving through that ground dissolves calcium and magnesium carbonates and arrives at your tap carrying them.
Across Thames Water's London supply that works out at roughly 250 to 350 milligrams of calcium carbonate per litre, which the Drinking Water Inspectorate classes as hard to very hard. It is entirely harmless to drink. It is simply inconvenient in every other respect.
When that water evaporates — on a shower screen, around a tap, on a tiled wall — the dissolved minerals stay behind. That is limescale. It is not dirt, and no amount of ordinary cleaning will shift it.
Why scrubbing makes it worse
Limescale is harder than most of the surfaces it forms on. Attacking it with an abrasive cream or a scouring pad takes some of it off and takes some of the chrome, glass or enamel with it.
The damage is cumulative and it is self-defeating: a micro-scratched surface holds the next deposit better than a smooth one did. A shower screen that has been scrubbed for two years will scale faster than a new one, and it will never fully clear again.
The answer is chemical, not mechanical. Limescale dissolves in acid — citric, formic or sulphamic depending on the deposit — applied at a controlled dilution and given time to work rather than force.
The marble problem
Here is the difficulty with prime London bathrooms specifically. The thing that dissolves limescale is an acid. The thing that permanently etches marble, limestone and travertine is an acid. And in most of the bathrooms we work in, the scaled chrome and the polished stone are within a hand's width of each other.
So descaling in a stone bathroom is a sequencing job. Stone is isolated and protected before anything is opened. The descaler goes on the fittings, glass and sanitary ware only, at a controlled dilution with a dwell time. Everything is then rinsed to neutral and dried.
That last step matters more than people expect. Air-drying hard water is precisely how the scale got there in the first place — every drop left to evaporate deposits its minerals exactly where it sat.
What helps between cleans
- Dry the shower screen after use. A squeegee takes fifteen seconds and does more than anything else on this list.
- Dry around taps and the base of fittings, which is where deposits concentrate.
- Keep acidic descalers away from any natural stone, full stop.
- Consider a softener if the house has repeated appliance problems — though be aware it changes how water feels and tastes, and it is a plumbing decision rather than a cleaning one.
- Have scale dealt with properly twice a year rather than fought weekly.
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