Our data
Certified vs. "tested to NSF standards"
Of 538 reduction claims for the contaminants we track across 96 water filters, 239 (44%) rest on the brand's own lab tests with no certifier listing, and 299 are certified by NSF, WQA, IAPMO or CSA. 58 of the 96 filters make at least one claim that is "tested" but not certified.
Certified means an accredited certifier tested the product, lists the exact model and each reduction claim in a public database, and audits the factory to keep the listing. "Tested to" means the brand paid a lab to run a test once and reports the result; nobody lists or re-checks it. Both can be true; only one can be looked up.
Counts cover the 18 contaminants on this site only; many filters carry more listings (taste, odor, particulates). Checked 2026-10-23. Free to cite with a link (CC BY 4.0).