The hardness at which water leaves limescale in a kettle measures 200 mg/L as CaCO₃ of total hardness, the level World Health Organisation Guidelines 2017 identify as scale-forming, per Drinking Water Inspectorate — Water Hardness / Hard Water, including what it says hard water does (read 20 September 2026).
Source: Drinking Water Inspectorate — Water Hardness / Hard Water, including what it says hard water does — read 20 September 2026
Drinking Water Inspectorate (DWI) enforces the UK drinking water quality regulations in England and Wales. Figures it classifies or regulates on this page cover England and Wales only.
What this page is, and what it is not
This page collects what the regulator's own page says about one thing in a house, printed in full, alongside the hardness figures this site holds for the areas it can answer for. It is a record of what is published, not advice about what to do.
There is no method here for removing anything. Nothing read and dated by this project publishes one, and a procedure written from general knowledge under our own byline would be the one thing on the page with nothing behind it.
Why the figure below is about your water, not about your house
The hardness of a supply is measured and published by the company that supplies it. How much deposit that produces in any particular appliance also depends on how hot it runs, how often, and how long the water sits in it — none of which is published by anybody, and none of which this site measures.
So the figures here describe the water. Where a comparison is drawn against a published level, it is a comparison between two numbers somebody else printed, and the sentence says whose they are.
What the regulator names, and in which sentence
The Drinking Water Inspectorate's own page on water hardness names kettles among the things hard water scales.
Every passage that names it, in full
Hard water causes scaling in hot water systems, kettles, electric irons and domestic appliances.
Source: Drinking Water Inspectorate — Water Hardness / Hard Water, including what it says hard water does — read 20 September 2026
Some activated carbon jug filters also contain ion exchange resin beads which alter the “temporary” hardness of water so that the filtered water has a lower tendency to form scum on the top of hot drinks like tea and they may minimise scale build up in kettles. These devices do not alter the permanent hardness of the water.
Source: Drinking Water Inspectorate — Water Hardness / Hard Water, including what it says hard water does — read 20 September 2026
The hardness at which water produces scale
DWI relays a figure from World Health Organisation Guidelines 2017, and states it like this:
The World Health Organisation Guidelines 2017 identified that water with a hardness of value of 200 mg/l or higher (measured as CaCO3 calcium carbonate) will produce scale and soft water with a value of 100 mg/l (as CaCO3 calcium carbonate) or less will be more corrosive to pipework.
Source: Drinking Water Inspectorate — Water Hardness / Hard Water, including what it says hard water does — read 20 September 2026
DWI classifies 200 mg/L as CaCO₃ as Moderately hard (150–200).
Your own water
How much scale forms starts from the hardness of the water arriving at your own stop tap, and this site holds a measured figure for 39 supply zones, published by 2 of 18 water suppliers. Most postcodes resolve to a supplier that publishes none, and the checker says so rather than estimating one.
Check what we hold for your postcode
Lichfield
The figure published for this area is 167.4–280.5 mg/L as CaCO₃, which is partly below that level and partly at or above it.
This supply runs 167.4–280.5 mg/L as CaCO₃, varying by supply zone. That spans DWI’s Moderately hard (150–200) to Hard (200–300) bands, so no single band describes it.
Hardness figure: South Staffordshire Water — supply-zone water quality reports — dated 31 December 2025, read 20 September 2026
What nobody publishes, and what we will not write
At what hardness does limescale become a problem?
What was looked for: a hardness above which a United Kingdom authority says scale becomes a problem, or a rate at which it says scale forms. Where: the Drinking Water Inspectorate's own consumer page on water hardness, which is the page that publishes the five-band scale and the hardness at which water will produce scale.
What it says instead: “The Drinking Water Directive and the UK drinking water quality regulations do not specify standards for hardness, calcium or magnesium.”
This site states none — not at 280.5 mg/L as CaCO₃, the hardest figure on this page, and not at any other figure.
What would change this: a UK regulator, a UK standards body or a UK statutory guideline stating a hardness at or above which scale is treated as a problem. The World Health Organisation figure the regulator relays is about scale forming in water, not about a level at which anybody should act, and this site states it as the former.
Source: Drinking Water Inspectorate — Water Hardness / Hard Water, including what it says hard water does — dated 20 September 2026, read 20 September 2026
What does limescale cost?
What was looked for: a figure for what scale costs — an efficiency penalty as a percentage, an appliance life in years, or a price for descaling or for replacing what scale shortened. Where: the Drinking Water Inspectorate's own consumer page on water hardness, which is where the effect is stated, and this project's own committed price observations, of which there are none for this country.
What it says instead: “Scaling of heating elements shortens their life and makes appliances less efficient.”
What would change this: a UK regulator, a UK energy body or a named study measuring the efficiency penalty or the appliance life, plus dated prices for what any of that would be multiplied by. Both are outstanding, so every line here states the effect in the regulator's words and attaches no number to it.
Source: Drinking Water Inspectorate — Water Hardness / Hard Water, including what it says hard water does — dated 20 September 2026, read 20 September 2026
How do you remove it?
What was looked for: a method for removing scale from a kettle, a toilet or any other appliance, published by a United Kingdom authority. Where: the Drinking Water Inspectorate's own consumer page on water hardness, which is the UK regulator's consumer page on the subject and the page that answers the softening question directly.
What it says instead: “Please read our Domestic water filters and softeners leaflet”
What would change this: the leaflet that sentence points at, which no task in this split has read, or another UK authority publishing a descaling method. Until one of those is read and dated, this site describes what scale is and where an area's water sits, and publishes no method of its own.
Source: Drinking Water Inspectorate — Water Hardness / Hard Water, including what it says hard water does — dated 20 September 2026, read 20 September 2026