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Data coverage and reporting periods

These counts describe the latest approved report held for each source area. They are not a count of homes tested or a claim of complete UK coverage.

Approved source-area coverage
SupplierAreasWith measured hardnessLatest periods held
Affinity Water92922025
Northern Ireland Water66662023, 2025
Severn Trent Water218382024, Rolling report 2025-08-01 to 2026-07-31; hardness period not stated, Rolling report 2025-09-01 to 2026-08-31; hardness period not stated
Scottish Water3693682016, 2017, 2018, 2019, 2020, 2021, 2022, 2023, 2024, 2025
Thames Water2452452024, 2025
United Utilities5756Rolling 12 months; updated 2026-09-04, Rolling 12 months; updated 2026-10-02, Rolling 12 months; updated 2026-10-16
Wessex Water44402025, Reporting period not retained in the cached source
Yorkshire Water33332024

Find Scottish Water hardness by supply-zone name

Town pages by supplier

3736 town pages use an approved report for the supply area associated with the town. The largest places are listed here; each supplier page lists all of its town pages. A town page does not confirm the supply at every address.

Thames Water: all 1066 town pages

Severn Trent Water: all 1357 town pages

Affinity Water: all 813 town pages

Wessex Water: all 404 town pages

United Utilities: all 62 town pages

Yorkshire Water: all 34 town pages

Postcode matching is a separate check

Thames, Affinity, Yorkshire, United Utilities and Severn Trent use their official lookups. Northern Ireland uses NI Water’s year-specific postcode file; some postcodes have multiple zones or no zone. We make uncertainty explicit. A town name or statistical boundary alone does not prove a supply-zone match.

How updates reach the site

Daily source checks detect new editions. Validated Thames formats can publish automatically; changed formats or investigation context need review. Other connectors retain source versions and use their own checks. The reporting year remains visible even when an older publication is the latest available. Wessex and Scottish Water currently require browser-based source review because hosted downloads are restricted.

Selected Yorkshire annual PDFs, United Utilities rolling reports and Severn Trent reports are checked weekly and published only after validating their identity, parameter inventory and units. Local examples show the exact supplier-checked postcode; this does not imply city-wide coverage.

Scottish Water’s official hardness tables cover 2016–2024. The latest hardness edition holds 277 named supply zones. Older or renamed zones remain historical records; names are not merged and these tables do not establish postcode boundaries. Use Scottish Water’s official postcode checker to identify your regulatory supply zone, then find that exact name below.

Incomplete legacy Yorkshire and United Utilities aggregates are withheld. Their raw sample datasets are being retained separately with dates and qualifiers; statistical-area samples must not become invented household or supplier-zone averages.

Official suppliers and current advice · Sources and methodology

Find a named source area

Use the exact zone or ward name from your supplier’s checker. These are published source areas, not postcode matches. Older areas may have been renamed or replaced; the latest reporting period we hold is shown for each.

1124 source areas match; showing the first 50.

Find your supplier’s official checker