To remove limescale, dissolve it with a mild acid: white vinegar or citric acid, left on long enough to work, then rinsed off with clean water. Taps need about an hour under a vinegar-soaked cloth, a shower head 4 to 5 hours in a bag of vinegar, and a kettle a single boil with vinegar and water. Never mix an acid descaler with bleach.
On this page
- Quick reference: what to use and for how long
- How much scale can a cup of vinegar dissolve?
- Kettle
- Shower head
- Taps and faucets
- Glass shower screens
- Washing machine and dishwasher
- Coffee machines
- Water heaters
- Toilets
- Safety: never mix acid with bleach
- Surfaces to keep acid away from
- Stopping it coming back
- Common mistakes
- Frequently asked questions
Limescale is mostly calcium carbonate, left behind when hard water is heated or dries. Acid turns it into a soluble salt and carbon dioxide (the fizzing you see), which is why kitchen acids work as well as many shop descalers on light scale. Below is what to use on each thing in your home, how much scale a cup of vinegar can actually dissolve, and the surfaces where acid does more harm than good.
Quick reference: what to use and for how long
| Where | What to use | Contact time | Method from |
|---|---|---|---|
| Kettle | Equal parts white vinegar and water, or 1–2 tbsp citric acid in a half-full kettle | Boil, then 15–20 min (citric) or until cool (vinegar) | Which? |
| Shower head | Plastic bag of white vinegar held on with a rubber band | 4–5 hours | Wessex Water |
| Tap spout | Cut lemon; for heavy scale, a cloth soaked in white vinegar | 1 hour (cloth) | Wessex Water |
| Shower screen | Half water, half white vinegar in a spray bottle | 1 hour | Wessex Water |
| Washing machine | 2 cups white vinegar, hottest cycle; then ½ cup baking soda, same cycle | Two empty cycles | Wessex Water |
| Tank water heater | Drain and flush with water | Until the hose runs clear | City of Anaheim |
| Tankless water heater | Undiluted white vinegar circulated through the unit | About 2 hours | City of Anaheim |
| Dishwasher, coffee machine | The descaler and program the manual names | Per the manual | Manufacturer |
How much scale can a cup of vinegar dissolve?
Acids don’t scrub limescale off; they react with it, and each molecule of acid can only dissolve so much. Two molecules of acetic acid (the acid in vinegar) dissolve one of calcium carbonate. Citric acid has three acidic groups, so two molecules dissolve three. From those ratios and the molar masses you can work out the most each one can dissolve:
| Descaler | Acid content | Limescale it can dissolve |
|---|---|---|
| 1 cup (237 mL) white vinegar, 5% acidity | 11.8 g acetic acid | 9.9 g |
| 1 cup vinegar at the 4% legal minimum | 9.5 g acetic acid | 7.9 g |
| 1 litre of 5% vinegar | 50 g acetic acid | 41.7 g |
| 10 g citric acid (about a tablespoon) | 10 g | 7.8 g |
| 100 g citric acid | 100 g | 78.1 g |
Two practical lessons come out of that table. First, a heavily scaled water heater element or a kettle with a thick crust can use up the acid before the scale is gone: if the fizzing stops and scale remains, pour it out and use fresh solution rather than leaving it longer. Second, gram for gram the two pure acids are close (0.83 g of scale per gram of acetic acid, 0.78 g per gram of citric acid), but vinegar is about 95% water. A tablespoon of citric acid powder does roughly the work of a cup of vinegar, which is why it suits kettles and coffee machines where you’d rather not leave a vinegar smell. Real results are lower than the maximum because the acid slows down as it weakens.
Kettle
Which? describes two easy methods. For vinegar, fill the kettle about three-quarters with equal parts white vinegar and water, boil, leave it to cool, then rinse. For citric acid, boil a half-full kettle of water, switch it off and unplug it, add one or two tablespoons of citric acid and leave it 15 to 20 minutes before pouring away.
Either way, finish by boiling clean water and pouring it out two or three times so nothing tastes of vinegar. Our step-by-step guide to descaling a kettle also works out how much acid a crust needs and how often to descale for your hardness. Wessex Water’s lemon version, with juice and lemon chunks left to cool for a few hours, is gentler and slower.
To slow the next build-up, Anglian Water suggests a wire scale collector in the kettle, and Wessex Water notes that scale tends to grip metal kettles less firmly than plastic ones.
Shower head
If the head unscrews, you can soak it in a bowl. If not, use Wessex Water’s bag method: fill a plastic bag with white vinegar, pull it up so the nozzles sit in the liquid, secure it with a rubber band and leave it 4 to 5 hours. Then scrub the nozzles with a brush and wipe with a damp cloth. Run the shower for a minute before using it to flush loose flakes.
Many shower heads have soft rubber nozzles. Rub them with a finger after soaking and the softened scale pops out.
Taps and faucets
For light marks, rub the spout with half a lemon. For heavier scale, Wessex Water suggests a cloth soaked in white vinegar wrapped around the area for an hour, then a wipe with a damp cloth. Unscrew the aerator at the tip of the spout if you can: it’s often where scale hides, and it soaks clean in a cup of vinegar.
Brushed, coloured or “matte black” finishes are often coatings rather than plain chrome. Check the care sheet for your tap before soaking it in anything acidic.
Glass shower screens
Rub the glass with a halved lemon, then spray with a half-and-half mix of water and white vinegar, leave it for an hour and wipe off with a damp microfibre cloth, Wessex Water suggests. A squeegee after each shower stops the drops drying, and dried drops are where scale starts. More detail, including stubborn and etched glass: hard water stains on shower glass.
Washing machine and dishwasher
For a washing machine, Wessex Water recommends spraying the door seal and drawer with white vinegar and wiping them, then running the hottest, longest cycle empty with 2 cups of vinegar in the detergent drawer, followed by a second cycle with half a cup of baking soda in the drum.
Dishwashers are different: many have their own softener. Keep the salt and rinse-aid compartments filled and set the hardness level in the unit your manual uses, Wessex Water advises. Our hardness converter turns your water report’s mg/L into German, French or Clark degrees. For descaling, use the product and program the manual names.
Coffee machines
Follow the manual. Espresso machines and pod machines have pumps, seals and heating blocks that the maker has tested with specific descalers and concentrations, and many machines have a descaling program that runs the solution through at the right pace. Many also ask for your water hardness to set how often they remind you to descale. Enter the real figure rather than leaving the factory default.
Water heaters
Scale and sediment collect at the bottom of a tank heater, where they cause rumbling noises and lower efficiency. The City of Anaheim, whose water is high in minerals, recommends draining sediment from a tank heater every 6 months and descaling tankless units once a year.
The flush in short: turn the gas to “pilot” or switch off the breaker, close the cold water inlet, attach a hose to the drain valve, open the temperature and pressure relief valve at the top of the tank, and drain until the water runs clear. A tankless unit is descaled by circulating undiluted white vinegar through it for about 2 hours, usually with a small pump and isolation valves.
The water comes out very hot, and the city warns that it can scald. If you aren’t comfortable with gas valves and electrical breakers, this is a job for a plumber, and your heater’s manual always takes priority over general steps.
Toilets
Scale builds up at the waterline and under the rim. Lower the water level first (turn off the supply and flush once), then pour white vinegar or a citric acid solution onto the marks, leave it a few hours and scrub. Never pour vinegar into a toilet that has a bleach block in the cistern or bleach gel in the bowl. That brings us to the one rule that matters.
Safety: never mix acid with bleach
The New Jersey Department of Health warns that mixing chlorine bleach with an acid produces chlorine gas, and that bleach plus vinegar gives off vapours “which can burn the eyes and lungs”. The same warning covers bleach with lemon juice and with toilet bowl cleaners. If you’ve used a bleach product, rinse it away thoroughly before any descaler goes near it, and keep the room ventilated.
Wear gloves with shop-bought descaling liquids, which are stronger than kitchen acids, and read the label before use, Which? advises.
Surfaces to keep acid away from
Marble, limestone and other calcium-based stone are chemically close to limescale, so the same acid that dissolves scale etches them. Stone-care maker Fila warns that vinegar, lemon and limescale removers can dull polished marble or leave rough white marks. Wipe scale on stone with a damp cloth often instead, and use a cleaner labelled safe for natural stone.
Also check the maker’s advice before using acid on enamel baths, rubber seals in older appliances, and plated or coated fittings.
Stopping it coming back
Limescale returns at a rate that tracks your water hardness. In a very hard area like Las Vegas (16 gpg), a kettle crusts up in weeks. If cleaning feels like a losing battle, you have three options:
- Dry what you can. A squeegee on glass and a cloth on taps prevents most visible scale, because scale forms where drops evaporate.
- Treat the water where it’s heated. A scale collector in the kettle, filtered water in the coffee machine, the correct hardness setting on the dishwasher.
- Soften the whole house. A softener removes the calcium and magnesium before they reach any tap. Start with what size water softener you need and how much salt it will use.
Not sure how hard your water is? Our guide to what hard water is explains how to find the figure.
Common mistakes
Leaving vinegar for days. Once the acid is spent, more time does nothing for the scale and may harm seals. Replace the solution instead.
Scraping with metal. Knives and wire wool scratch kettles, glass and chrome, and scratches give new scale a rough surface to grip.
Forgetting to rinse. Acid left on a heating element or in a coffee machine can affect taste and, over time, the parts. Rinse or run clean water through twice.
Using the wrong unit on appliances. Enter 20 because your water company quotes 20 French degrees, when the dishwasher wants German degrees (that’s 11.2 °dH), and it uses far more salt than it needs. Convert first.
Frequently asked questions
Is vinegar or citric acid better for limescale?
Both work. Citric acid does more per spoonful and leaves no smell, so it suits kettles and coffee machines. Vinegar is cheap, easy to buy by the litre, and handy for soaking shower heads and taps.
Is limescale harmful?
No. Which? notes limescale is harmless to consume, though it can affect taste, and Anglian Water says the scum it leaves on tea is harmless. The damage is to appliances, not to you.
Can I leave vinegar in a kettle overnight?
It isn’t needed. A boil and cool-down usually does the job, and if scale remains it means the acid is used up, so fresh solution helps more than extra hours.
What dissolves heavy limescale fastest?
A stronger acid, which is why shop descalers work faster than vinegar. They’re also harsher, so follow the label, wear gloves and keep them off stone and coated finishes.
How do I get limescale off a glass shower door?
Spray it with equal parts water and white vinegar, leave it an hour, then wipe with a damp microfibre cloth. Rubbing it with a lemon first helps on thick spots.
Why does limescale come back so quickly?
Because the water keeps bringing more. The harder your water, the faster it returns. A household of four on water as hard as Las Vegas’s sends more than 100 kg of dissolved minerals through its pipes each year.
Sources
- Wessex Water: Limescale
- Which?: Five simple ways to remove limescale from your kettle
- City of Anaheim: Hot water heater maintenance
- New Jersey Department of Health: Hazard alert, mixing cleaners (PDF)
- US FDA: CPG Sec. 525.825, vinegar definitions
- Anglian Water: Water quality fact sheet, hard water (PDF)
- Fila: Acid etching on natural stone
