How We Score & Recommend Filters
Transparency matters on a YMYL site. Here is exactly how our tools work.
Data Sources
Product specs
Every filter in our database is researched from the manufacturer's official product page and spec sheet. We record NSF certifications, flow rates, filter life, replacement costs, dimensions, and pricing. Each product has at least one source URL pointing to the official spec sheet.
NSF certifications
We verify certifications against NSF International, WQA, and IAPMO databases where possible. Each certification in our data is marked as verified (confirmed in a third-party database) or unverified (manufacturer claim only). Products that claim "tested to NSF standards" but lack formal product certification are flagged with a note explaining the distinction.
Contaminant data
EPA Maximum Contaminant Levels (MCLs) come from the National Primary Drinking Water Regulations. PFAS limits use the April 2024 EPA Final Rule (4 ppt for PFOA/PFOS). Health effect descriptions are sourced from EPA assessments and use conservative, factual language.
Water quality data
Water system contaminant levels come from the EWG Tap Water Database (which aggregates EPA SDWIS data) and individual utility Consumer Confidence Reports (CCRs). We cover 100 US water systems serving 90+ million people across 3,038 ZIP codes.
How the Contaminant Matcher Scores Filters
When you enter a ZIP code, the Contaminant Matcher:
- Looks up your water system - matches your ZIP to one of 100 curated public water systems
- Retrieves detected contaminants - from the most recent testing data available for that system
- Filters eligible products - only includes filters with at least one verified NSF certification (products without any verified cert are excluded)
- Matches contaminants to filters - checks which of your detected contaminants each filter is certified or claimed to reduce
- Scores and ranks - each matched filter gets a 0-100 score based on four factors
Scoring breakdown (0-100 points)
What percentage of your detected contaminants does this filter address?
More verified NSF standards = higher trust. Each verified cert adds 7.5 points.
Lower ongoing cost scores higher. Not the dominant factor - certification matters more.
Lower upfront cost gets a small bonus. This prevents expensive systems from dominating when a cheaper one works.
Commission rates are not a factor. A filter paying 15% commission is scored identically to one paying 3%. The algorithm has no access to commission data.
Products We Exclude
- xProducts with no NSF certification at all are excluded from the Contaminant Matcher (e.g., Berkey, which uses internal testing only). They may still appear on comparison and editorial pages with clear disclosure.
- xProducts claiming "tested to NSF standards" without formal certification are included but flagged. Their unverified claims do not contribute to the NSF breadth score.
- xDiscontinued products are excluded from all tool results but may remain in editorial content for reference.
Data Freshness
Product prices are checked and updated periodically. Each product card shows a "Price checked" date so you can judge freshness. Contaminant data uses the most recent available testing year (typically 2023-2024). We aim to refresh all product data quarterly and water quality data annually.
Found an Error?
If you find incorrect data, a broken link, or a missing product, email hello@waterfiltermatch.com. We take data accuracy seriously - especially on a health-adjacent site.