How we rank water filters
We are certification-first. A filter earns a place in our data because an independent body lists it as reducing a specific contaminant — not because a brand says "tested to" a standard, and not because anyone paid us.
Certification is a gate, not a weight
Every filter in our database is listed in the public certification directories of NSF, WQA (Gold Seal), or IAPMO. If a product isn't listed by one of these bodies for a given contaminant, we don't credit it with removing that contaminant — no exceptions, regardless of marketing claims.
This matters because the single most common trick in water filtration is the phrase "tested to NSF/ANSI Standard 53." That is not the same as being certified. Certification means the exact model appears in the certifier's database with a listed claim. "Tested to" means a company ran its own test and is telling you about it. We only count the former.
Certification is per-contaminant
"NSF certified" is not one thing. A filter certified under NSF/ANSI 53 for lead is not automatically certified for PFAS, arsenic, or fluoride. NSF/ANSI 42 is an aesthetic standard — it covers taste and chlorine, not health contaminants. On every product page we show the exact list of contaminants a filter is certified to reduce, and we state plainly that it does not imply removal of anything not on that list.
The number we lead with: true cost per gallon
Sticker price is misleading. A $20 pitcher or fridge filter is often the most expensive water you can buy per gallon, because its cartridge is rated for only a few hundred gallons. We compute cost per gallon from the certified capacity and current retail price so you can compare a pitcher to a whole-house system honestly. Cost-per-gallon figures are our estimates and are labeled as such.
Our data sources
- Filter certifications: NSF, WQA, and IAPMO public certified-product listings.
- What's in your water: EPA's Safe Drinking Water Information System (health-based violations, 2016+) and the UCMR5 national PFAS monitoring program. Both are public domain.
- Prices & photos: retailer listings, matched to the certified model and shown only when we can confirm the match is the real product (not an aftermarket "compatible" cartridge).
What we refuse to do
- No star ratings on unverifiable claims. The certified facts carry the weight.
- No "best" list without the sorted, sourced data that proves it.
- No promoting alkaline, "structured," hydrogen, or magnetic-descaler pseudoscience.
- No recommending a filter as a fix for microbially unsafe water (bacteria, boil-water situations) — that is not what point-of-use filters are for.
- No letting affiliate payment change a ranking. Rankings are by certified coverage and cost per gallon; buy links are added after.
Found something wrong? Certification listings change. We regenerate our data from the primary sources; if a fact looks off, it is worth checking the source listing linked on the product page.