How We Test & Check

“Checked” is in our name, so here’s exactly what it means. Every filter, reverse osmosis system and softener we cover goes through the same four passes before we publish a word of opinion about it. If a product fails a pass, the review says so — including when the failure is “we could not verify this claim at all.”

1. Certifications, verified per exact model

We look up the specific model — not the brand, not a sibling product — in the official NSF and IAPMO/WQA listing databases. We record which standard it is certified to (NSF/ANSI 42 for aesthetic effects like chlorine taste, 53 for health contaminants such as lead and PFAS, 58 for reverse osmosis systems, 401 for emerging compounds, 44 for softeners) and whether the listing covers the complete system or only a component. A membrane certified to NSF 58 inside a system that is not itself certified gets reported as exactly that. Marketing badges, “tested to NSF standards” language and self-issued certificates are treated as unverified claims and labelled as such.

2. Published lab data, cited — never invented

Where independent laboratory results exist (for example, certified-lab tap-water analyses published by testing services and review labs), we cite them with the source named on the page. We distinguish clearly between three grades of evidence: independent lab testing, manufacturer testing, and manufacturer claims with no test behind them. Where we have not physically tested a product ourselves, our pages say “research-based” plainly. We would rather show you slightly less information with its source attached than a confident number with none.

3. True-cost math, in the open

For every system we calculate five-year cost of ownership: purchase price, replacement filters or membranes at the manufacturer’s stated intervals, softener salt, waste water from RO recovery rates, regeneration water for softeners, and electricity where it applies. We show cost per year and, for drinking-water systems, cost per gallon. The inputs and arithmetic are published with the result — if you think we’ve got an input wrong, the contact page is where to tell us, and confirmed errors are corrected on the page with a note.

4. No pay for placement — ever

Brands cannot pay for a ranking position, a “best” label, a review, or the removal of a negative finding. Affiliate commissions differ between programs, and we treat that as a conflict to manage, not a compass: recommendations are written from passes 1–3 first, and affiliate links are attached afterward. Where we have a commercial relationship with a brand we cover, the disclosure page describes how that works in full.

Corrections & updates

Certifications change, models get revised, and prices move. We re-check listings when we update a guide, date our updates, and correct errors in the open rather than silently editing them away. If you spot something we’ve got wrong, we want to hear it — accuracy is the entire product here.