Answers to the questions we hear most — about the data, the certifications, the tools, and how this site makes money. Something we have not covered? Email waterbythebook@gmail.com.
Is everything on this site free?
Yes. Every guide, every tool and every data study is free to use. There is no paywall and no account to create.
Where do your water-quality numbers come from?
From the EPA’s own public data — the UCMR5 monitoring results and the SDWIS compliance database — not from press coverage or vendor material. Every figure we publish states its data vintage, and our national studies are computed by committed scripts over public-domain data, with the method and caveats published alongside.
Can you tell me whether my water is safe to drink?
No, and we will not pretend otherwise. What we report is what a water system reported to the EPA. That is occurrence data: it is not a compliance ruling, not a health verdict, and system-level data is not a statement about your particular tap. For health questions, talk to your doctor or your local health department.
How do you decide which filter to recommend?
By certification, not by marketing. We check filters against the NSF, IAPMO and WQA listing databases, and we always distinguish NSF-LISTED (verifiable in the database) from manufacturer-claimed. You can see the whole set in the Filter Certification Registry.
Will a filter remove lead, or PFAS?
Only if it is certified for that specific contaminant — “filter” on the box means very little on its own. A pitcher certified for taste and chlorine is not certified for lead. Look for certification against the standard that covers the contaminant you care about (NSF/ANSI 53 is the one for lead), and check the listing rather than the packaging. The registry shows which claims are verifiable.
Do you make money from the filters you recommend?
Yes, and here is exactly how: some outbound links are affiliate links, and as an Amazon Associate we may earn from qualifying purchases. It costs you nothing extra and it never changes which filter we say fits. Affiliate links are marked sponsored/nofollow. See the affiliate disclosure.
What do the tools actually do?
Which Filter Fits narrows you to the cartridge that fits your fridge or system. Water Watchdog returns what your own water system reported, by ZIP. The reverse-osmosis cost calculator and the water-softener sizing calculator estimate running costs and sizing. Always confirm the model stamped on your unit before buying.
Who writes this site?
Every guide is written under the editorial byline Thomas Kwayne — a pen name for the site’s editorial process, not a fabricated expert. No invented credentials and no stock-photo author. More on the About page.