How we check

We combine two kinds of public records: what EPA’s testing found in a utility’s water, and what certification bodies list for a filter. We do not test water and we do not test products. Every number on the site links to the record it came from.

Water data

• Which systems: the 50 largest active community water systems by population served in EPA’s Safe Drinking Water Information System (SDWIS), read through EPA Envirofacts. One record (Tri Town Water Board, MA) was left out because SDWIS lists about ten times the people the three towns it serves have.
• Violations: SDWIS health-based violations whose compliance period began in the last 10 years, with EPA’s own names for each code.
• PFAS and lithium: EPA’s final UCMR 5 dataset (29 PFAS and lithium, sampled 2023–2025, released August 2026). We compare it with the limits the way EPA’s own UCMR 5 data summary does: each sampling point with a full set of samples is averaged, results below the reporting level count as zero, and the average is rounded to the limit’s significant digits. This is a screening comparison, not a compliance finding; compliance is judged on running annual averages from 2029.
• Limits: PFOA and PFOS 4.0 ng/L; PFHxS, PFNA and HFPO-DA 10 ng/L; and a hazard index of 1 for PFAS mixtures, all in 40 CFR 141.61(c). On 20 May 2026 EPA proposed rescinding the last four (Federal Register 2026-10085) and letting systems ask for until 2031 on PFOA and PFOS (2026-10086). Neither is final as of 16 Oct 2026. Lithium has no limit; EPA’s 10 µg/L figure is a screening level.
• Places and ZIP codes: the ZIP codes each system reported to EPA for UCMR 5, named with GeoNames postal data (CC BY 4.0).

Filter claims

For each of the 97 products we read the brand’s own product page and, where the brand publishes one, its performance data sheet, and recorded every reduction claim word for word with the page address and the date. Then we looked for the model, its replacement filter and the brand in the IAPMO R&T listing directory, one search at a time.

• Certified means a current listing shows that claim for that exact model or its replacement filter, under a named standard (NSF/ANSI 42, 44, 53, 55, 58, 401 or CSA B483.1). Materials-only listings (NSF/ANSI 61 and 372) never count as a reduction claim.
• Brand says certified means the brand says the claim is certified, but the IAPMO listing does not show it. Many products are certified by NSF or WQA instead. Their sites’ terms do not allow automated lookups, so those listings are checked by hand, one model at a time, and each check is recorded with its date. Until then, every product page links you straight to the NSF and WQA searches for that model.
• Brand claim means the brand says the product reduces something without saying it is certified for it (“tested”, “removes”, “reduces”).

“PFAS” on its own is broader than “PFOA and PFOS”. Where a brand says PFAS but the listing covers only PFOA and PFOS, the product page says so.

What we don’t do

• We don’t test products or water, and we never imply that we did.
• We don’t let commissions change a label. A label comes only from a listing.
• We don’t show prices: they change daily and some stores allow prices only from their own feeds.

Spotted an error? Tell us and we will check it against the listing.