How we verify

1. We look up each manufacturer on NSF's public Drinking Water Treatment Units listings (info.nsf.org/Certified/DWTU/) for NSF/ANSI 42, 53, 58 and 401.
2. We record only the models, replacement elements, rated service cycle, flow rate and contaminant claims exactly as NSF lists them, and link the listing on every page.
3. If a product is not on NSF's listing we do not call it NSF-certified, even if packaging says "tested to NSF standards". Some brands certify through IAPMO or WQA instead; we don't cover those yet, so a missing ✓ means "not on NSF's listing", not "uncertified everywhere".
4. Filter prices come only from the manufacturer's own store, with the date we saw them.

Last full check: 2026-10-17. We do not test products, publish reviews or ratings, or give health advice.