If you live anywhere with hard water, your kettle is almost certainly carrying a layer of limescale. It looks like a chalky white-grey film on the inside of the spout and the heating plate, it slows the boil, and over time it can shorten the kettle's life. The good news is you can shift it in twenty minutes with a single lemon.

Why lemon works

Limescale is mostly calcium carbonate, deposited as the water heats. Citric acid, which is what lemons are full of, reacts with calcium carbonate and dissolves it. Vinegar does the same job through acetic acid, but lemon leaves no smell, no aftertaste in the next cup of tea, and is safe on stainless-steel and plastic kettle interiors.

What you need

  • One lemon (or two tablespoons of bottled lemon juice in a pinch).
  • Cold tap water.
  • A clean cloth or kitchen paper.

The method

  1. Slice the lemon into rough wedges and drop them into the empty kettle. Squeeze the wedges as you go to release the juice.
  2. Fill the kettle to the maximum line with cold water.
  3. Bring the kettle to the boil. Switch off and leave the lemon water to sit for at least 15 minutes; an hour is better for heavy build-up.
  4. Pour out the water and lemon. Use a soft cloth to wipe the inside of the kettle. Loosened limescale should come away easily.
  5. Rinse the kettle two or three times with cold water. Boil one further full kettle and discard the water before using normally.

How often

In a hard-water area such as London, the South East or much of East Anglia, descaling once a month is sensible. In soft-water areas (most of Scotland, Wales and the North West) every two to three months is usually enough.

Lemon vs vinegar vs descaler

Vinegar is slightly stronger but leaves a smell that can take several boils to clear. Branded descalers are stronger again and are the right choice for kettles that have been ignored for years, but for routine maintenance lemon is the cheapest and least disruptive option.

Common mistakes

Do not use a metal scourer on the heating plate; you will scratch the surface and create new sites for limescale to deposit on. Do not skip the rinse boil at the end. And do not try this on a kettle that is still hot from a recent boil, drop the lemon into a cold kettle for safety.