How we verify things
Most sites in this field assert a hardness figure and move on. This page shows the working instead — including the times we were wrong.
The problem with water hardness data
There is no free, openly licensed, postcode-level water hardness dataset for the UK. Every water company publishes a figure for your postcode on their own site, but those tools are not open data and scraping them is not permitted.
So this site does not claim to know your exact hardness. It identifies your supplier, states the band their supply falls in, and sends you to their own official checker for the number. That is legal, useful, and honest about its own limits — and it is enough, because the advice changes at band boundaries rather than at single mg/l.
There is no single UK classification
This surprised us. Checking all 23 suppliers found four different published schemes:
| Published by | Bands | "Soft" means |
|---|---|---|
| Drinking Water Inspectorate, Thames Water | 5 | up to 100 mg/l |
| Bristol Water, South West Water | 6 | 0–50 mg/l |
| Southern Water | 4 | under 100 mg/l |
So the same water can be called slightly hard by one company and moderately soft by another, without either being wrong. We follow the Drinking Water Inspectorate's classification because the DWI is the regulator, and we say so rather than quietly picking one.
What "verified" means here
Two different things, kept separate on purpose:
- Band verified (12 of 23). We read the supplier's own page and their description of their own water matches the band we show. The quote, its source and the date are on their page.
- Figure verified (0 of 23). Nobody. Companies publish hardness per postcode, not as a company-wide number, so there is no published figure to check against. We therefore show no number at all rather than an estimate dressed up as data.
Six claims we reduced
Checking suppliers against their own words found that we had overstated hardness in six places — always in the same direction. Each page carries the correction.
| Supplier | We said | Corrected to |
|---|---|---|
| Anglian Water | Very hard | Hard |
| Cambridge Water | Very hard | Hard |
| Portsmouth Water | Hard | Moderately hard |
| SES Water | Very hard | Hard |
| Severn Trent Water | Hard | Moderately hard |
| Thames Water | Very hard | Hard |
The most consequential was Severn Trent, whose own factsheet says their supply ranges from soft to moderately hard. Correcting it removed the water softener pages for Nottingham, Leicester, Coventry and Birmingham — the site had been recommending a softener into water its own supplier calls soft.
Where we stopped
9 suppliers could not be verified, and the reason is the data rather than the effort: they publish a postcode lookup and no description of their supply as a whole. Rather than leave that as a task that never closes, each records why. Two more are NAV suppliers that buy water in bulk and do not determine their own hardness at all.
The same standard applies to us
The directory refuses to show an accreditation badge for an installer unless an editor checked the official register. It would be incoherent to hold installers to that and not ourselves, so this site claims experience, not qualifications: no accreditation or registration is asserted anywhere, because none is recorded. See our editorial policy.