A shower running eight minutes a day at ten litres a minute puts roughly twenty-nine thousand litres through the head in a year. At the 280 to 300 milligrams per litre of dissolved calcium carbonate that most of London gets out of the tap, that’s about eight and a half kilos of chalk passing across your tiles annually, looking for somewhere to sit down.
Some of it does. That’s the whole subject.
I get asked whether eco products can handle it about twice a month, usually by somebody who has bought a £6 plant-based descaler, sprayed it at a shower screen, wiped it off after thirty seconds and concluded that eco cleaning is a scam. The product was probably fine. What they did with it wasn’t.
What Is London Limescale, and Why Won’t It Wipe Off?
Calcium carbonate, mostly, with some magnesium in the mix.
London water comes off chalk and limestone aquifers carrying calcium bicarbonate in solution. Heat it, or let it evaporate on a surface, and the bicarbonate converts and drops out as a solid carbonate crystal. That crystal doesn’t rest on the glass. It nucleates and grows into the micro-texture of whatever it landed on, keying into the surface the way frost keys into a windscreen.
Which is why wiping does nothing and why scrubbing is the wrong instinct. You cannot scrub calcium. You can abrade it, and on a shower screen that means taking off the scale plus a layer of the glass, which is how screens end up with that permanent cloudy zone at hip height that no product touches afterwards.
Every cream cleaner, every green scourer, every “miracle” sponge from the pound shop works by abrasion. They do shift the deposit. They also shift the surface it’s sitting on, and glass doesn’t grow back.
The Difference Between Scale and Soap Scum
A shower screen carries two deposits and people treat them as one thing.
Scale is the mineral, and it needs acid. Soap scum is calcium and magnesium bound to the fatty acids in soap – an insoluble salt with an oily character – and it needs a detergent or a mild alkali. Attack a screen with acid alone and you get a partial result, because the acid has to travel through a greasy film to reach the mineral underneath.
Order matters. Wash first with a drop of washing-up liquid to lift the soap layer, then acid, then rinse. Most failed descaling in bathrooms is acid applied to the wrong side of a barrier.
Do Eco Limescale Removers Work, or Are They Weak by Design?
They work, and the reason people think otherwise is the packaging rather than the chemistry.
Eco-certified descalers – EU Ecolabel, Nordic Swan, the credible schemes – use organic acids. Citric, lactic, gluconic, sometimes acetic. Citric acid does two jobs at once: it donates hydrogen ions like any acid, and it chelates, meaning the molecule grabs calcium ions and holds them in solution so they can’t redeposit. That second mechanism is the one the harsh mineral acids don’t have, and it’s why a citric solution keeps working on a dirty surface where a stronger acid gives up.
The problem is concentration and format. A ready-to-use eco spray is typically ninety-five per cent water sitting somewhere around pH 3. The trade descaler under my sink is sulphamic acid at pH 1, and pH runs on a logarithmic scale, so that’s a hundredfold difference in hydrogen ion concentration.
You can close that gap with time and heat, which are free. You cannot close it in thirty seconds, which is what the label’s picture of a smiling woman implies you’ll need.
The Trigger Spray Problem
Spray a vertical shower screen and the liquid is in the tray in under twenty seconds. The product had no contact time because gravity took it away, and the customer concludes it’s weak.
Soak a sheet of kitchen roll in the solution and press it flat onto the glass. Leave it thirty minutes. Come back, peel it off, rinse. That’s the whole technique and it converts a mediocre eco spray into something that outperforms a strong acid used badly. For tap bases and shower heads, a freezer bag and an elastic band does the same thing overnight.
Which Acid Does the Job, and at What Strength?
Citric acid is the one I’d have in the house if you only wanted one.
A kilogram tub costs about £8 from a trade counter or a brewing supplier and makes an absurd amount of solution. For scale, mix 10 to 15 per cent by weight into warm water – 100 to 150 grams per litre, which is far stronger than any bottled eco product and still costs pennies. Warm is worth emphasising. Reaction rate climbs sharply with temperature, and a solution at 50°C does in twenty minutes what a cold one takes an hour over.
Lactic acid turns up in the better commercial eco descalers and is kinder to gloss surfaces, with a slight residual film that beads water afterwards. Worth buying pre-made rather than mixing.
Sulphamic acid is what’s in most kettle descaler sachets and in the trade products. Not eco-certified, low volatility, no fumes, and it will handle a decade of scale in a WC pan. It also pits chrome if you leave it sitting.
Hydrochloric acid belongs in thick toilet gels and nowhere else in a domestic bathroom. It gasses off, it attacks chrome, and one splash on a stone floor is permanent.
Vinegar sits at the bottom of this list and I’ve written elsewhere about why.
The Kettle, Done Properly
Twenty grams of citric acid, kettle filled with hot water from the tap, stirred, left twenty minutes, then boiled once and emptied. Rinse three times.
Don’t add the powder and boil immediately – citric foams hard and you’ll have it across the worktop. And the third rinse is the one people skip before ringing to say the tea tastes of lemons.
What Will the Acid Wreck If You Get It Wrong?
Anything carbonate-based, which is a longer list than the bathroom suggests.
Marble, travertine, limestone, terrazzo and the cement-bodied encaustic tiles in half the hallways south of the river all dissolve on contact, and the damage is etching rather than staining – material gone, dull patch, mason’s job. Cement grout erodes the same way, more slowly. A shower floor treated with strong acid monthly will have soft, sandy grout lines inside two years, and then the acid is reaching the adhesive bed.
Chrome plating tolerates a short contact and dislikes a long one. Anodised aluminium, unlacquered brass, and the brushed-gold taps that arrived in every London refurb after 2019 are all vulnerable, and the finish on those is a coating rather than a metal. Test on the underside of the spout.
Then the one that ends the conversation. Glass under long-term scale leaches silica at the contact points, and once that’s happened the surface is etched beneath the deposit. You remove the scale and the cloudiness stays, because it’s in the glass now. No product recovers it. Polishing compounds with cerium oxide can improve a small patch and will introduce optical distortion across a large one.
The Screen in Acton I Couldn’t Save
Nine years, no squeegee, hard water, a tenant who’d been using a cream cleaner on it since 2016. She wanted a deep clean and was ready to pay for three hours.
I acid-treated a hundred-millimetre test patch by the handle, left it forty minutes, rinsed, and showed her. The scale came off. The haze didn’t move. I charged her nothing and told her a replacement panel was somewhere around £150 fitted, which is less than I’d have taken off her for a job that couldn’t work. You cannot scrub calcium, and you certainly cannot scrub the hole it left behind.
Can You Stop It Coming Back Without a Water Softener?
Mostly, yes, and I’d argue the squeegee beats the softener on value in any flat you don’t own.
Deposition happens when water evaporates on a surface. Remove the water before it evaporates and there’s no mineral left behind. A squeegee costs about £6, lives on a suction hook inside the cubicle, and takes eleven seconds after a shower. A household that does this has no screen scale at all – not less, none – and it makes the difference between a bathroom I can clean in twenty minutes and one that takes fifty.
Softeners are a real fix and a real commitment: £800 to £1,500 installed, a drain connection, cupboard space, and £60 to £80 a year in salt. In an owned house with a family and a combi boiler, the sums work, because scale on a heat exchanger costs efficiency and eventually costs a boiler. In a rented one-bed, no.
Magnetic and electronic “conditioners” that clamp to the pipe are the thing I’d argue about at a trade counter. The independent evidence for them is thin to absent, the manufacturers’ testing is mostly their own, and I’ve been in three London kitchens with one fitted and scale on every tap. I’d spend the £200 on a new shower head and a squeegee.
What a Weekly Clean Does and Doesn’t Do
Here’s the bit that costs me money to say. My weekly visit does not prevent limescale, and hiring a cleaner is close to useless against it.
I arrive on a Thursday, seven days of deposition are already crystallised onto the glass, and I spend fifteen minutes of your two hours removing what a squeegee would have prevented in seventy-seven seconds of the customer’s own time. That’s a bad trade for you. Do the eleven seconds a day and I’ll spend the fifteen minutes on your oven, which is a job you can’t do in a towel.
Quarterly, unscrew the tap aerators and drop them in a cup of citric solution overnight. Monthly, bag the shower head. Everything else is daily and takes less time than finding the remote.
The tub in my van is marked with a biro line at the halfway point so I know when to order more, and it’s been going down about a centimetre a month since February.