Transparency
Our Methodology
Every number, score, and recommendation on ClearWaterScore is built on a transparent, reproducible methodology. This page explains exactly how we source data, calculate water quality scores, and evaluate filtration products. If you find an error or disagree with our approach, we want to hear from you.
Data sources
EPA SDWIS (Safe Drinking Water Information System) — Our primary data source. SDWIS contains compliance monitoring data for every public water system in the United States, including contaminant levels, violation history, and system information. This is the same data that water utilities report to federal regulators. We pull directly from EPA's data services and update our database quarterly.
EWG Tap Water Database — We use the Environmental Working Group's health guidelines as a second benchmark alongside EPA MCLs. EWG's guidelines are typically stricter than EPA limits because they're based solely on health research without considering treatment feasibility or cost. We present both standards so you can make an informed judgment.
NSF International — All product performance claims are verified against NSF's certified product database. NSF certification means the product has been independently tested in an accredited lab and proven to remove contaminants to the level claimed. We do not rely on manufacturer claims alone.
Utility Consumer Confidence Reports (CCRs) — We cross-reference EPA data with individual utility CCRs for editorial context and any locally-reported data not yet in SDWIS.
Water quality scoring
Each city receives a ClearWaterScore from 0-100 based on a weighted assessment of its water quality data. The score is not a simple pass/fail against EPA limits — it incorporates the EWG health guidelines, violation history, number of contaminants detected, and the severity of any exceedances.
The scoring formula weights five factors:
How many detected contaminants exceed EWG health guidelines, and by how much.
Whether any contaminants exceed federal legal limits — the most serious finding.
Number and severity of EPA violations in the past 10 years.
Total count of contaminants found above detection limits.
Whether the system uses protected surface water, groundwater, or vulnerable sources.
Scores are categorized as: Good (75-100), Fair (50-74), or Poor (0-49). A "Good" score does not mean the water is perfect — it means the detected contaminant levels are relatively low compared to both EPA and EWG benchmarks. Even cities with good scores may have specific contaminants worth filtering.
Product evaluation
Every filter and treatment system is rated on a 10-point scale across five equally weighted criteria:
Products without NSF certification for their claimed contaminant removal are automatically penalized. We do not accept products for review from manufacturers, and we do not share content with manufacturers before publication.
Affiliate disclosure
ClearWaterScore earns affiliate commissions through Impact and CJ Affiliate when you purchase products through our links. Commission rates vary by brand (typically 6-15%) but do not influence our ratings or recommendations. Our editorial team does not know commission rates when evaluating products. Products are ranked by performance score, not revenue potential.
We disclose affiliate relationships on every page that contains product links. If we recommend a product that doesn't have an affiliate program, we still recommend it — we just don't earn from that recommendation.
Corrections and updates
We update city water quality data quarterly as new EPA SDWIS data becomes available. Product reviews are updated when manufacturers release new models or change specifications. If we publish an error, we correct it promptly and note the correction at the top of the affected page.
If you find an error in our data or disagree with our methodology, please contact us at hello@clearwaterscore.com. We take accuracy seriously and appreciate corrections.