How We Research

Every guide on The Water Filter Lab is researched and written by The Water Filter Lab Editorial Team from published, checkable sources. We do not run lab tests or hands-on testing. We don't measure contaminant removal, flow or taste ourselves, and we don't publish our own test results, star ratings or scores. What we do instead is below.

Our research process

1. Start with the water problem. We identify the contaminant or issue the guide is about (lead, PFAS, chlorine taste, well-water iron, hardness and so on) and what the EPA says about it.
2. Find the standard that covers it. We work out which NSF/ANSI standard addresses that contaminant. NSF/ANSI 42, for example, covers taste and odor, while lead and PFAS reduction fall under NSF/ANSI 53 or 58.
3. Check certification listings. We look up each candidate model in the NSF, WQA and IAPMO R&T listings to confirm exactly which contaminants it is certified to reduce. A model being certified for one thing doesn't mean it's certified for another.
4. Compare specs and running costs. From manufacturer spec sheets and retailer listings we compare capacity, flow rate, filter life, installation needs, price and replacement-filter cost.
5. Name the gaps. We say what a filter does not remove and where its certification stops, because that is usually what matters most.
6. Label every claim by source. Certified performance is described as certified. A claim that rests only on a manufacturer's own or commissioned testing is described as the manufacturer's claim.
7. Keep it current. We revisit pages when listings, products, prices or regulations change, or when a reader reports an error, and we update the page's “Updated” date when we make a substantive change.

Sources, in the order we trust them

1. Independent certification listings (NSF, WQA Gold Seal, IAPMO R&T). A listing ties a specific model to a specific standard and contaminant. This is the strongest evidence we use, and it outranks anything on the box.
2. Government and public data: EPA drinking water regulations and contaminant limits, and utilities' annual water quality reports. We use these to explain what is in tap water and what levels matter.
3. Manufacturer spec sheets and performance data sheets. Reliable for physical facts such as dimensions, capacity, flow and filter life. Performance claims that go beyond the certification listing are reported as the manufacturer's claim, not as fact.
4. Retailer listings. Used for current price, availability and replacement-filter cost. Prices change often, so treat any price on our pages as a snapshot.

We don't treat marketing copy, star ratings or “tested to remove 99%” badges as evidence of performance unless an independent certification backs them up.

Use of AI

We use AI tools to help draft articles; every factual claim is checked against the sources listed above, and pages are corrected when we find errors.

Money and independence

We earn affiliate commissions on some links (see our affiliate disclosure). Commissions don't change our picks, and we recommend products we have no affiliate relationship with when they are the better fit.

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