How We Review Water Filters
We buy and use every filter we review, and we check every certification claim against the listings. We do not run lab tests. Here is exactly what we do.
The review process
We buy it
We buy every filter we review at retail, the same way you would. No brand pays for placement.
We use it at home
Pitchers go into daily use for drinking water. Under-sink systems go on a kitchen tap. Where we report a measurement, such as a TDS meter reading, a flow rate or an install time, we say what we measured and when.
We check every certification claim in three directories
NSF, IAPMO and WQA all certify water filters to the same NSF/ANSI standards, and many filters appear in only one of them. We search all three by company and by model number, and record the listing and the date. A claim we cannot find in any listing gets no credit in our scoring, whatever the box says.
We score it on a published formula
The seven weighted categories below produce the overall score. Contaminant reduction, the largest share, is set by the certification listing, not by our own impression.
Scoring framework
Each reviewed product receives a weighted score from 0 to 10 across seven categories. The overall score is a weighted average.
| Category | Weight |
|---|---|
| Contaminant Reduction (NSF/ANSI 53, 58) Set by what a certifier lists: lead and PFAS 10, lead 8, TDS only 5, NSF/ANSI 42 only 4, no listing 2 | 35% |
| Taste & Odor (NSF/ANSI 42) Chlorine, taste and odor listing, plus our own daily use | 15% |
| Value vs. Price Purchase price relative to certification level, filter life, and annual cost of ownership | 15% |
| Annual Operating Cost Filter replacement cost per gallon over rated filter life at household of 4 usage | 15% |
| Installation & Ease of Use Time to install, tools required, filter replacement process, user interface | 10% |
| Flow Rate & Convenience GPM for under-sink/whole-house; fill time for pitchers; tank capacity for countertop RO | 5% |
| Build Quality & Warranty Materials, fit and finish, warranty length, replacement part availability | 5% |
What we do not do
We do not send filtered water to a lab, so no review on this site reports a lab result of ours. A TDS meter measures total dissolved solids only. It cannot detect lead, PFAS, bacteria or most contaminants people buy filters for, so we never use a TDS reading as evidence for any of them.
If you want to know what is in your own water, a lab test is the way to find out. Our Tap Score review covers one option you can order yourself.
Affiliate disclosure
H2O Insider earns affiliate commissions when readers purchase products through our links. We participate in the Amazon Associates program and direct affiliate programs with select brands. These commissions pay for the filters we buy and for running the site.
Affiliate relationships do not influence our scores or recommendations. Our scoring formula is applied identically to all products regardless of affiliate availability. If the best product in a category has no affiliate program, we recommend it and link to it without a commission. Brands cannot pay to improve their ranking or remove negative findings.
Corrections
We correct factual errors promptly. If a certification claim is wrong, a listing has changed, or a product has been discontinued, we update the review and note the date of correction at the top of the article. We do not silently revise published content.
To report an error, email editorial@h2oinsider.com with the URL and the specific claim you believe is incorrect.