The 35 supply zones South Staffordshire Water publishes a hardness figure for runs 136.3–351.8 mg/L as CaCO₃, varying by supply zone, which spans DWI's Slightly hard to Very hard bands, per South Staffordshire Water — supply-zone water quality reports (31 December 2025, read 20 September 2026).
Source: South Staffordshire Water — supply-zone water quality reports — dated 31 December 2025, 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 hard water is, and what it is not
Hard water is water carrying dissolved calcium and magnesium, picked up from the chalk and limestone it moved through on the way to the tap. It is not a contaminant and it is not a safety question: the drinking water regulations set no limit for hardness at all, which is why the regulator publishes a scale for describing it and nothing to comply with.
What it changes is your kettle, your boiler and how much detergent a wash needs. That is a cost question rather than a health one, and it is the reason this cluster exists.
Hardness is set by your supply zone, not by your town
Water companies divide their areas into supply zones, and a zone is defined by where the water is taken from and how it is treated. Two streets in one town fed from different sources sit in different zones, and can sit in different bands on the table below.
So a figure for a town is an average of things that are not the same, and an average of two zones is a number neither of them measured. Where this site holds more than one zone for an area it prints the range and names both ends rather than splitting the difference.
Why this page is organised by water company
There is no national hardness dataset in this country. The regulator publishes the band table and no values, so every figure here comes from a water company's own supply-zone report — and coverage follows what each company chooses to publish, not where people live.
A company that publishes its zones as a list can be read in full. A company that hands out a figure only after a postcode is typed cannot be read at all without asking it one postcode at a time, which is not something this site does to somebody else's website. Where that is the case, the row says so, with the address that was read and the day it was read.
What a row with no figure means, and what it does not
A company with no figure in the table below is not a company whose water is soft, and it is not a company without supply zones. What is missing is a published list this site can read. The row states that, with the evidence, instead of a zero.
Nothing here is estimated to fill a gap, and no figure is carried over from a neighbouring zone. Where we hold no measurement, the page says we hold no measurement.
How DWI describes hardness
| Band | mg/L as CaCO₃ |
|---|---|
| Soft | up to 100 |
| Slightly hard | 100–150 |
| Moderately hard | 150–200 |
| Hard | 200–300 |
| Very hard | more than 300 |
The scale above is Drinking Water Inspectorate’s own, and every figure on these pages is banded against it rather than against a scale of ours.
Source: Drinking Water Inspectorate — Water Hardness / Hard Water ("Water Hardness (mg/l CaCO3)") — dated 20 September 2026, read 20 September 2026
What we hold today
Counted from the table below: 39 supply zones carry a published figure. The table covers 18 water companies, which is every one this country holds, and they fall into 4 groups.
- Publishes a list we can read in full: 1
- Answers one address at a time, so what we hold is a bounded sample: 1
- No supply-zone figure of theirs is held here: 14
- Outside every source this programme holds: 2
Every one of the water companies, and what we hold for it
| water companies | What we hold | Source | What the company itself publishes |
|---|---|---|---|
| South Staffordshire Water | 136.3–351.8 mg/L as CaCO₃ — 35 supply zones, read from the company's own annual zone reports. | Source: South Staffordshire Water — supply-zone water quality reports — dated 31 December 2025, read 20 September 2026 | — |
| Yorkshire Water | 47.9–370.6 mg/L as CaCO₃ — 4 supply zones from 6 postcode lookups of the company's own checker — a bounded sample, not a published list. | Source: Yorkshire Water — Water quality report for 1st January 2024 - 31st December 2024 — dated 31 December 2024, read 20 September 2026 | — |
| Affinity Water | Affinity Water publishes a hardness figure for each of its supply zones, and none of them is among the figures this page holds yet. | Source: Affinity Water — the page probed for its supply-zone hardness, which answered HTTP 200 — dated 20 September 2026, read 20 September 2026 | — |
| Anglian Water | Anglian Water publishes a hardness figure for each of its supply zones, and none of them is among the figures this page holds yet. | Source: Anglian Water — the page probed for its supply-zone hardness, which answered HTTP 200 — dated 26 September 2026, read 26 September 2026 | — |
| Dŵr Cymru | Dŵr Cymru publishes no supply-zone hardness we can read: probed on 20 September 2026 its hardness page answered HTTP 200, and the only route to a figure is its own postcode lookup, one request at a time. | Source: Dŵr Cymru — the page probed for its supply-zone hardness, which answered HTTP 200 — dated 20 September 2026, read 20 September 2026 | — |
| Hafren Dyfrdwy | Hafren Dyfrdwy publishes a hardness figure for each of its supply zones, and none of them is among the figures this page holds yet. | Source: Hafren Dyfrdwy — the page probed for its supply-zone hardness, which answered HTTP 200 — dated 26 September 2026, read 26 September 2026 | — |
| Northumbrian Water | Northumbrian Water publishes a hardness figure for each of its supply zones, and none of them is among the figures this page holds yet. | Source: Northumbrian Water — the page probed for its supply-zone hardness, which answered HTTP 200 — dated 20 September 2026, read 20 September 2026 | — |
| Portsmouth Water | We are not yet printing Portsmouth Water's hardness figures while we confirm whether they describe total hardness or calcium hardness alone. | Source: Portsmouth Water — the page probed for its supply-zone hardness, which answered HTTP 200 — dated 26 September 2026, read 26 September 2026 | — |
| SES Water | SES Water publishes a hardness figure for each of its supply zones, and none of them is among the figures this page holds yet. | Source: SES Water — the page probed for its supply-zone hardness, which answered HTTP 200 — dated 20 September 2026, read 20 September 2026 | — |
| Severn Trent Water | Severn Trent Water publishes a hardness figure for each of its supply zones, and none of them is among the figures this page holds yet. | Source: Severn Trent Water — the page probed for its supply-zone hardness, which answered HTTP 200 — dated 20 September 2026, read 20 September 2026 | — |
| South East Water | South East Water publishes a hardness figure for each of its supply zones, and none of them is among the figures this page holds yet. | Source: South East Water — the page probed for its supply-zone hardness, which answered HTTP 200 — dated 20 September 2026, read 20 September 2026 | — |
| South West Water | South West Water publishes a hardness figure for each of its supply zones, and none of them is among the figures this page holds yet. | Source: South West Water — the page probed for its supply-zone hardness, which answered HTTP 200 — dated 20 September 2026, read 20 September 2026 | — |
| Southern Water | Southern Water publishes no supply-zone hardness we can read: probed on 26 September 2026 its hardness page answered HTTP 200, and the only route to a figure is its own postcode lookup, one request at a time. | Source: Southern Water — the page probed for its supply-zone hardness, which answered HTTP 200 — dated 26 September 2026, read 26 September 2026 | — |
| Thames Water | Thames Water publishes no supply-zone hardness we can read: probed on 20 September 2026 its hardness page answered HTTP 200, and the only route to a figure is its own postcode lookup, one request at a time. | Source: Thames Water — the page probed for its supply-zone hardness, which answered HTTP 200 — dated 20 September 2026, read 20 September 2026 | Thames Water says “all the water in our region is hard”. Its own published scale puts Hard at 200–300 mg/L as CaCO₃. Published by: Thames Water — read 26 September 2026 |
| United Utilities | United Utilities publishes a hardness figure for each of its supply zones, and none of them is among the figures this page holds yet. | Source: United Utilities — the page probed for its supply-zone hardness, which answered HTTP 200 — dated 20 September 2026, read 20 September 2026 | — |
| Wessex Water | We are not yet printing Wessex Water's hardness figures, because we have not been able to read the figures it publishes on its own website. | Source: Wessex Water — the page probed for its supply-zone hardness, which answered HTTP 200 — dated 20 September 2026, read 20 September 2026 | — |
| Scottish Water | We hold no drinking-water data for Scotland. Every source this site reads — the water companies' published quality results, their supply-zone hardness reports, the regulator's supply-zone notices and the Environment Agency's storm-overflow return — covers England and Wales only. Scotland's drinking water is regulated separately, by the Drinking Water Quality Regulator for Scotland. | Source: Scottish Water — the source that names it as the public supplier — dated 19 September 2026, read 19 September 2026 | — |
| Northern Ireland Water | We hold no drinking-water data for Northern Ireland. Every source this site reads covers England and Wales only, and Northern Ireland's drinking water is regulated separately, by the Drinking Water Inspectorate for Northern Ireland. | Source: Northern Ireland Water — the source that names it as the public supplier — dated 19 September 2026, read 19 September 2026 | — |