How WaterByTheBook decides what to publish, where the numbers come from, and what we refuse to claim. Last updated 28 July 2026.
Primary sources only, for anything numeric
Filter certifications are checked against the NSF, IAPMO and WQA listing databases — the actual registries, not the box copy. We always distinguish NSF-LISTED (verifiable in the database today) from manufacturer-claimed, because those are different things and the difference is usually the whole story.
Water-quality figures come from the EPA’s public data: the UCMR5 monitoring results and the SDWIS compliance database. Every figure we publish carries its data vintage, because “PFAS was detected” means something different in 2023 data than in 2026 data.
Occurrence, never verdict
This is the line we hold hardest. When we report monitoring data, a system reported above a limit. That is not a compliance ruling, not an enforcement finding, and not a health verdict. System-level data is also not a claim about your particular tap — what arrives at your kitchen depends on your service line and your building.
For what your own utility reported, use the Water Watchdog lookup rather than inferring it from a state-level figure.
No medical advice
We report what the EPA limit is and what systems reported against it. We do not tell anyone their water is safe, and we do not tell anyone their water is making them ill. Those are questions for a doctor or a local health department, and a website that answers them from a spreadsheet is doing something dishonest.
Trade-offs named out loud
Every recommendation on this site has a downside, and we print it: reverse osmosis wastes water to drain; aftermarket cartridges are cheaper but the certification has to be checked individually; a softener will not fix heavy iron on its own; the correct answer is sometimes that you do not need a filter. Confirm the model stamped on your own equipment before buying — always.
Reproducible data work
Our national studies are computed by committed scripts over public-domain EPA data, not assembled by hand. The method, the denominators and the caveats are published with every study, so a reader who disagrees with a number can see exactly how it was produced and check it. The underlying data is public domain; the analysis and presentation are ours, and attribution is requested.
Corrections
We would rather be corrected than be wrong quietly. If a figure, a certification listing or a fitment on this site is wrong, email waterbythebook@gmail.com with the page and what looks off. We check it against the source, fix it if it is wrong, and where the error was material we say on the page what changed and when. Data that has been superseded gets updated with its new vintage rather than silently left to rot.
Who writes this
Guides are published under the editorial byline Thomas Kwayne. That is a pen name for the site’s editorial process — not a fabricated expert. There are no invented credentials here, no borrowed job titles and no stock-photo author, because a made-up specialist is exactly the kind of thing this site exists to argue against. What we claim is what we do: research against primary sources, stated plainly. More on the About page.
How these pages are produced
Research, drafting and fact-checking on this site are AI-assisted, working against the primary sources named above — the NSF, IAPMO and WQA certification listings and the EPA’s UCMR5 and SDWIS data — under human editorial direction and review before anything is published. We say so because a page arguing against invented expertise has no business being coy about its own process.
What that does not change: every number traces to a named source with its vintage stated, the certification claims are checked against the registries rather than the packaging, and no claim appears here that we could not point you at. Those rules are the reason to trust a figure on this site — not who, or what, typed it.
Independence
The site is funded by affiliate commissions, disclosed in full on the affiliate disclosure page. No manufacturer pays for coverage, a ranking or a review, and no commission changes which filter we say fits. See also our privacy policy.