Data sources
Where everything on this site comes from, under what licence, and when we last checked it.
Water company published water quality reports
Licence: Published by each company under their statutory duty. Individual figures may be quoted with attribution; bulk reuse is not licensed.
How we use it: The authoritative source for a specific postcode. We link readers to each company's own checker rather than reproducing their data.
Last checked 2026-08-04
Drinking Water Inspectorate
Licence: Open Government Licence for most publications — check each document.
How we use it: Regulatory standards, annual compliance reports, and guidance on what is actually in UK drinking water. Used for the standards and compliance content, not for postcode-level hardness.
Last checked 2026-08-04
Postcodes.io
Licence: Open source (MIT), built on ONS and Ordnance Survey open data under the Open Government Licence.
How we use it: Postcode validation, geocoding, and mapping a postcode to its district, county and region. Every postcode lookup on the site goes through it.
Last checked 2026-08-04
Ordnance Survey Code-Point Open
https://www.ordnancesurvey.co.uk/products/code-point-open
Licence: Open Government Licence, attribution required.
How we use it: Not yet used. The self-hosting option if Postcodes.io ever becomes a dependency risk — see STRATEGY.md.
Last checked 2026-08-04
Companies House public data and API
https://developer.company-information.service.gov.uk/
Licence: Open Government Licence.
How we use it: Verifying a company number given during installer registration or a profile claim. Not used to generate listings — a registered plumbing company is not the same thing as a water filtration installer, and listing one as such would be a claim we cannot support.
Last checked 2026-08-04
WaterSafe register
Licence: No reuse licence. Public search only.
How we use it: Manual check by an admin when an installer claims WaterSafe registration. We link to the register so readers can confirm it themselves. Not scraped, not bulk-imported.
Last checked 2026-08-04
What we deliberately do not use
Being clear about this matters as much as listing what we do use.
- Checkatrade, Rated People, MyBuilder, Trustpilot, Google Business Profile. Their terms do not permit reuse of their listings or reviews. We do not scrape them and we do not import from them.
- The WaterSafe, WIAPS and TrustMark registers as data. We check them by hand when verifying an individual installer's claim, and we link readers to them. We do not bulk-extract them into our directory.
- Water company postcode hardness tools. These are not open data. We link to them; we do not scrape them, and we do not reproduce their per-postcode figures.
- Companies House as a source of listings. We use it to verify a company number someone has given us. We do not generate installer listings from SIC codes — a registered plumbing company is not the same thing as a water filtration installer, and listing one as such would be a claim we cannot support.
Where our hardness data has limits
There is no openly licensed postcode-level water hardness dataset for the UK. We therefore identify your supplier and the band their supply typically falls in, and link you to their own official checker for the precise figure. Company-level entries in our data carry a verified flag; where it is false, the site shows the band and withholds the number rather than guessing at it.
If you spot something wrong, tell us.