How we verify product data

Where the facts come from

Sources are ranked, and the rank decides. When two sources disagree, the higher one wins and the disagreement is recorded rather than averaged away.

1. 1. A certification body's own listing

   The only record that shows a product was tested by an accredited third party against a published standard. It is the evidence, not a description of it.

2. 2. The manufacturer's datasheet or installation manual

   Written for installers and warranty claims, so its numbers — flow rate, pressure range, capacity, connection size — are the ones the brand is accountable for.

3. 3. The brand's own product page

   Current and specific, but written to sell. Used for facts the datasheet omits, and never to settle a performance question a certification listing can answer.

4. 4. Tier-1 journalism

   Used for recalls, litigation and company events, where a newsroom has done reporting the brand has no reason to publish.

5. 5. A retailer listing

   Used for price and availability, which is what a retailer actually knows. Never for performance claims.

6. 6. An owner forum thread

   Used only for lived experience — what breaks, what the install really took — and only from a thread opened and read in full, never from a link we have not confirmed points where we say it does.

Every field on a product page carries the source it came from and the date that source was read, so you can follow any number back to the document it was taken from.

Independent re-derivation

1. A different job, with no memory of the first

   Verification runs as a separate job in a fresh context. It receives the finished record and its citations, and nothing else — not the research notes, not the reasoning, not the order the facts were found in. It has to arrive at each value again from the source, so it is a re-derivation rather than a proofread. A checker that can see the working will agree with the working.

2. Every cited source is re-opened live

   Each field's source is fetched again at verification time. The verdict for that field is one of: confirmed, contradicted by the source, not found in the source, source no longer reachable, or source changed since it was read. A field only stays on the page as stated if the live source still supports it.

3. Certification claims are re-checked against the directories, not against us

   Both positive and negative certification statements are re-checked directly in the certification bodies' own directories. Our own certification index is never the authority for this step: a snapshot can only tell you what was true when it was taken.

4. Every purchase link is opened

   The verifier follows each affiliate destination and confirms the landing page is this exact brand and model. A link that resolves to a search page, a discontinued variant or a different SKU does not ship.

What a page has to clear to publish

When a page passes, the result is published on the page itself: at the bottom of every product page, the sources section states how many fields were re-derived, how many of those were safety-critical, and the date the check ran.

Certification is checked live, in both directions

A certification statement is only as current as the lookup behind it, so every one on this site — that a product is listed and that it is not — is backed by a dated lookup made in the certification bodies’ own directories at verification time. We do not infer a certification from marketing copy, and we do not infer the absence of one from a product missing from a database we happen to hold.

We index listings from NSF International, IAPMO R&T and WQA Gold Seal, which are three of the accredited certification bodies. Others certify to the same standards — UL Solutions and CSA Group among them — and we do not index those yet. If a product is certified only by a body we do not index, it can be missing from our results while being genuinely certified. That is a gap in our coverage, not evidence about the product, and we say so on the page rather than letting the blank speak for itself.

A listing carries the same weight whichever body issued it. The standards themselves — NSF/ANSI 42, NSF/ANSI 53, NSF/ANSI 58, NSF/ANSI 401 and the rest — are written through ANSI’s consensus process; the bodies that certify products against them are accredited separately, by ANAB in the United States. Under one standard, no certifier outranks another, and we never present one directory as the complete record of what is certified.

What a brand advertises and what a body has listed are shown side by side on every product page, never merged into one claim. Where they differ, the difference is the point. The certification index has its own methodology page, covering how those listings are gathered and refreshed.

Blanks are published, with their reasons

When we cannot establish a fact from an acceptable source, the field stays blank and the reason is published beside it. It is never estimated, inferred from a similar model, or filled in from general knowledge.

Every product page ends with the full list of what we could not establish and why. “The manufacturer does not publish cartridge dimensions” tells you something a blank cell never could: that the gap is theirs, that we looked, and that you will not find it elsewhere either.

Prices and ratings carry their date

Prices move, and a price with no date is a claim about today that was true on some other day. Every price, rating and review count on a product page is shown with the date it was read, so a stale figure looks stale instead of looking current. Cost-of-ownership maths — replacement schedules, dollars per year, ten-year totals — is built from those dated figures and shows its inputs.

How the links are handled

Product pages carry affiliate links, and we earn a commission when someone buys through one, at no extra cost to them. That relationship is disclosed next to every purchase button.

It changes nothing about what the page says. The research and verification steps above have no access to the commercial fields of a record, so no fact is reached with a commission in view, and no product is ordered, recommended against or left out because of what a link pays. Full affiliate disclosure.

What this method does not give you

It is a documentation method, not a laboratory. We do not test products ourselves, and nothing here should be read as our own performance measurement. What we can tell you is exactly what an accredited body has listed, exactly what a manufacturer has committed to in writing, and exactly where the two diverge.

We also cannot verify a claim whose source has gone. When a cited page disappears or changes, the field is flagged and re-checked rather than quietly kept. If you find something on a product page that is wrong, we would rather hear about it than keep publishing it.