How to descale a kettle: citric acid, vinegar and how often

Before you start

Check the manual first: some models give a specific descaling method or warn against certain products, and a removable limescale filter usually needs rinsing separately. Morphy Richards advises never using bleach or antibacterial cleaners inside a kettle. Never mix bleach with vinegar or a limescale remover; Which? warns that the combination can create toxic gas. Never fill above the kettle’s maximum line, and unplug it before emptying or rinsing.

Method 1: citric acid

Citric acid is sold as a white powder in supermarkets and hardware shops. Which? describes this method:

1. Half-fill the kettle with water (no higher than the maximum line) and boil it.
2. Carefully add one to two tablespoons of citric acid. It may fizz as it reacts with the scale.
3. Leave it for about 15 to 20 minutes.
4. Pour the solution away and rinse the kettle at least twice.
5. Boil a kettle of fresh water and pour it away before you make a drink. Repeat the whole process if heavy scale remains.

Method 2: white vinegar

The vinegar method takes longer and leaves a smell, so rinsing matters. Which? suggests equal parts white vinegar and water, filled to about three-quarters; Morphy Richards suggests half water and half white vinegar, left for 20 to 30 minutes after boiling.

1. Fill the kettle to about three-quarters, and no higher than the maximum line, with a 50:50 mix of white vinegar and water.
2. Boil it, then leave it to stand for 20 to 30 minutes or until cool.
3. Empty it and rinse several times.
4. Boil and discard fresh water once or twice to remove the vinegar taste.

Method 3: a shop-bought descaler

Use a product that says it is suitable for kettles and follow the pack instructions exactly, including the dose and contact time. Which? advises wearing gloves and reading the instructions before starting. Rinse and boil fresh water afterwards. Which? and Morphy Richards also describe a lemon juice method: boil a kettle of water with lemon juice added, leave it for 20 to 30 minutes and rinse thoroughly.

How often to descale, by water hardness

Morphy Richards’ general rule is every one to three months: monthly in very hard water areas and about quarterly in moderately hard areas. Which? suggests about once a month, and more often for glass kettles in hard water areas. Neither gives a fixed rule for soft water. Use these as starting points, then descale whenever you can see a white or chalky layer on the element or base. The bands below are the DWI hardness bands, in mg/l as calcium carbonate:

• Soft (up to 100 mg/l): little scale is expected; descale when you see deposits.
• Slightly hard (100–150 mg/l): check every few months and descale when deposits appear.
• Moderately hard (150–200 mg/l): about every three months, following Morphy Richards’ guidance.
• Hard (200–300 mg/l): every one to two months is a sensible starting point within the one-to-three-month range.
• Very hard (over 300 mg/l): about monthly, as both guides suggest.

Check your area’s published hardness · Hard water areas in the UK · Convert hardness units (mg/l, °Clark, °dH) · Water hardness in London · Water hardness in Sheffield · Water hardness in Leeds · Water hardness in Manchester

If your hardness is in a different unit

Supplier reports and appliance manuals use different units. 100 mg/l as calcium carbonate is about 7 °Clark (English degrees) or 5.6 °dH (German degrees). Use the converter to move your published figure into mg/l before comparing it with the bands above. Hardness varies within a region, and a supply-area figure is not a test of the water at your own tap.

Ways to slow the build-up

Which? suggests emptying the kettle after each use rather than leaving water standing in it; Thames Water also suggests emptying the kettle if you are not using it for a while and using a steel scale collector. DWI says some jug filters that also contain ion-exchange resin may minimise scale build-up in kettles, although they do not remove permanent hardness; check what your specific cartridge claims to reduce. Only boil the water you need. A whole-house softener is a much bigger decision, covered in the guides below.

Is kettle scale harmful?

Water hardness is not a safety grade. Thames Water says the minerals in hard water are not considered harmful, and DWI notes some limited evidence linking hardness with cardiovascular health. Scale mainly affects taste, appearance and how efficiently the kettle heats. If your water suddenly changes colour, taste or smell, contact your water supplier rather than descaling.

Related questions

• How to remove limescale from taps, shower heads, toilets and glass
• Do water filters remove limescale? Check what the filter does
• Hard water vs soft water: what the difference means
• How to soften hard water: options and practical checks