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Where UK water quality and hardness data is published

Local tap-water results come from your water supplier. Regulators check suppliers and publish national reports, but they do not give a result for your street. No single official source covers every UK postcode.

Who publishes what

Your supplier for drinking water can differ from the company that takes away wastewater. Check the name on the drinking-water part of your bill, or use our postcode search for the suppliers we cover.

Regulators and open-data portals

  • Drinking Water Inspectorate (DWI)

    Regulator · England and Wales

    Annual “Drinking water” reports with company performance data; consumer guidance, including hardness bands.

    Use DWI for regulation, company-level performance and guidance. DWI directs households to their water company for local hardness.

    Drinking Water Inspectorate (DWI) · DWI hardness guidance

  • Drinking Water Quality Regulator for Scotland (DWQR)

    Regulator · Scotland

    Annual reports on public and private water supplies, and how it checks Scottish Water’s sampling.

    Use DWQR for regulatory context. Local zone results come from Scottish Water.

    Drinking Water Quality Regulator for Scotland (DWQR) · Public water supply

  • Drinking Water Inspectorate for Northern Ireland (DAERA)

    Regulator · Northern Ireland

    Annual report on public and private drinking-water supplies in Northern Ireland.

    NI Water is the public supplier; the Inspectorate regulates and reports on its results.

    Drinking Water Inspectorate for Northern Ireland (DAERA) · 2024 report announcement

  • OpenDataNI

    Open-data portal · Northern Ireland

    NI Water’s annual hardness by supply zone, customer-tap results, public registers and postcode-to-zone lookup.

    Download the files for the year you need. These are NI Water’s own results, published through a government portal.

    OpenDataNI · data.gov.uk record

  • Stream

    Open-data portal · England and Wales

    Water-industry open datasets. Some companies list domestic water-quality data here.

    Check each dataset’s publisher, period, geography and licence before using it.

    Stream

DWI’s hardness guidance gives a general England and Wales picture and tells households to ask their water company for accurate local figures. It is not a postcode-level dataset.

Official supplier lookups

This list covers the 19 suppliers and regional brands WaterGrade has profiled. It does not yet include every licensed supplier; for example, Northumbrian Water and Essex & Suffolk Water are not listed. Each link goes to the supplier’s own water-quality page. Where WaterGrade imports a supplier’s reports, we note the geography, period and hardness unit it uses. For other suppliers, read these from your result.

England

Wales

Scotland

Northern Ireland

If your supplier is not listed, check the drinking-water supplier named on your bill and use its website. All supplier guides

What the reporting periods mean

  • Calendar year: most annual zone reports summarise samples taken from January to December. The year printed in the report is the period; a year inside a zone’s name may be different.
  • Rolling window: some checkers summarise the last 12 months (or a quarter or month you select) and update weekly. Two overlapping windows are not separate years, so do not read them as a trend.
  • Undated summaries: a “typical hardness” figure may have no stated sampling period. Treat it as a guide, not a dated measurement.
  • Different dates on one page: hardness and other quality results can come from separate publications with different periods.
  • An area summary, not your tap: results describe samples across a supply zone. They are not a test at your home and do not tell you about a problem happening now. For a current problem, contact your supplier.

What the units mean

  • mg/l as CaCO₃ (the same number as ppm) is the unit DWI uses for its hardness bands: soft up to 100, slightly hard up to 150, moderately hard up to 200, hard up to 300, very hard above 300.
  • mg Ca/l can mean total hardness expressed as calcium. Multiply by 2.5 for mg/l as CaCO₃. A separate calcium result is not total hardness.
  • French degrees (°fH) × 10 = mg/l as CaCO₃. Clark and German degrees and mmol/l are common in appliance manuals.
  • “Less than” values (for example <0.5) mean the result was below what the laboratory could report. It is not zero and not a measured value.
  • Sample counts tell you how many samples a summary is based on. Keep them with the result.

Convert between hardness units · How to read a water-quality report

Reusing the data

Being able to see a result does not mean you may copy it. NI Water’s files on OpenDataNI, and DWI and DWQR content, are published under the Open Government Licence. Suppliers’ website terms vary: Thames Water’s, for example, require written consent to copy content. Check the terms before republishing.

WaterGrade publishes an open dataset with NI Water’s zone hardness (under the Open Government Licence) and this list of sources as a download (CC BY 4.0).

Sources and review

Supplier links come from WaterGrade’s supplier guides, reviewed 6 September 2026. All links on this page were checked on 11 September 2026. Prepared by WaterGrade. Suggest a correction