Scoring methodology · Water filters

How we score water filters

Every water filter is evaluated against 4 rules, worth a total of 100 points. Your score is the percentage of points the product earns on what we actually know about it.

Active version: 2026.06.01

Quality score

Earned out of possible

Each rule contributes points up to a known maximum. We sum them, divide by the total possible, and that's the headline number on the product.

Unknowns

No data earns no points

If we couldn't verify an attribute, that rule earns zero. Brands aren't rewarded for non-disclosure, and we don't fill the gap with a guess.

The rules

4 rules · 100 points possible

Verified contaminant removal

verified_removal

max · 70% of score

Weighted average of measured removal across 15 contaminant categories. Each category carries a public-health weight; PFAS, heavy metals, radiologicals, and microbiologicals carry the most. Missing or null measurements count as 0% removal — to earn points the brand must publish actual lab data.

Citation: Category weights internal; per-category removal sourced from published third-party lab tests.
Inputs read: filtered_contaminant_categories

Lab data indexed

lab_indexed

max · 15% of score

A full third-party lab report has been indexed for this product. Without it, removal numbers come from manufacturer-submitted data and the verified-removal rule earns no points by default.

Citation: Oasis editorial — proxy for testing transparency.
Inputs read: is_indexed

Certified by a recognized body

certification_body

max · 10% of score

Product is certified by a recognized water treatment standards body — NSF, IAPMO, or WQA. We can't yet distinguish which specific standard (NSF 42 vs 53 vs 401), only that one of these bodies has certified the product.

Citation: NSF/ANSI standards; IAPMO R&T; WQA Gold Seal.
Inputs read: certifications

Filter technology disclosed

filter_technology_disclosed

max · 5% of score

The brand has disclosed what filter technology is used (e.g. activated carbon, reverse osmosis, KDF, ceramic). Rewards transparency; does not yet rank technologies against each other.

Citation: Oasis editorial — transparency credit.
Inputs read: technologies

Found something wrong?

Scoring is a function applied to evidence. If you think a rule fired on the wrong evidence, the per-product breakdown shows the source for every contribution — each one is challengeable. The methodology itself is version-controlled and evolves in public.