Limescale Explained

Jan 20, 2020

The chemical formula of the limescale-removing agent citric acid.

Limescale is a deposit of mainly calcium carbonate which forms when hard water (i.e., water that contains a high concentration of dissolved minerals) evaporates. It’s usually white and feels rough or scaly to the touch. Sometimes the deposits are reddish brown because they also contain iron compounds.

Limescale spoils the appearance of your bathroom fittings, making your shower door opaque and your taps crusty. Moreover, a limescale build-up can cause permanent damage to your bathroom. It eventually eats into the chrome of your taps to the point where it can’t be removed without stripping away the chrome as well. In toilets you can get an unsightly brown crust forming below the water line. Untreated limescale can be even more of a problem in dishwashers and washing machines, where it will literally block up the pipes.

Fortunately, limescale is relatively easy to control because calcium carbonate is soluble in acidic solutions. It can be removed with almost any type of acid, though the one you choose will probably be dependent on the degree of the problem. For a home remedy, you can spray vinegar onto affected areas or soak shower heads in vinegar. Personally, I don’t like having the bathroom smell like dill pickles, so I use another method. Various limescale removing agents include:

  • Citric acid (available on eBay as a crystalline powder)
  • Sulfamic acid (many commercial descaling solutions contain this)
  • Formic acid
  • Phosphoric acid (found in Coca Cola)
  • Sulphuric acid!
  • Hydrochloric acid!


To avoid damaging your chrome wear, I would recommend starting with a gentle, organic acid, such as acetic acid (vinegar) or citric acid. Citric acid is my first choice, as it’s non-toxic and has no odour. I mix it up at a concentration similar to lemon juice (about 60g/l). You can add it to water, but I usually add it to bathroom cleaner instead. The bathroom cleaner foams up, so that the solution clings to the lime-scaled areas better. Another advantage is that the citric acid-bathroom cleaner mixture will remove dirt and soap scum as well as limescale.

If you have a really crusty tap, the best option is probably to use a descaling gel such as Kilrock (currently £4-5 for a 160ml jar on Amazon). There is a handy brush in the cap, which makes the product easy to apply, even to shower heads. Descaling gels contain sulfamic acid, therefore must be rinsed off within the time period specified in the instructions.

Sulphuric acid and hydrochloric acid are strong (and dangerous) acids that should never be applied to taps or sinks. However, they are fantastic for removing limescale or “urine stains” from toilets. Urine encourages limescale because it’s alkaline, and that is why we observe staining in toilets not flushed after every use. “Acid Toilet Cleaner” from Firstcall Janitorial is a hydrochloric acid-containing product guaranteed to make the bowl white again.

All limescale removing products must be rinsed away after use because they are acidic and will corrode metal. Even vinegar, and limescale-fighting bathroom cleaners, must be rinsed off. The only anti-limescale products you don’t need to rinse off are the “daily shower cleaners”. These prevent limescale by chelating the calcium in the water, so that calcium carbonate doesn’t form. Though we don’t really need to know how they work…

Many of us find the fumes from daily shower cleaners unpleasant. I suspect the fumes are probably dangerous, hence the warning labels on the bottles which advise using only outdoors or in well-ventilated areas. I favour skipping the chemicals and simply drying the shower after use. A window squeegee and a cloth make quick work of this chore. You might throw up your hands in horror at the idea of drying the shower every time you use it. Fair enough. Any good cleaning service will remove limescale on a weekly or fortnightly basis in hard water areas.

Of course, limescale is only one of the cleaning challenges we face in hard water areas. The rough surface of the scale traps water and encourages the growth of mould. In my next blog I discuss how to foil the fungus!