How We Rank Water Filters
Every score on this site comes from the same published method, built on certification listings, not marketing claims.
The short version
We score each filter out of 5. Certified contaminant reduction counts for 40%, and a claim earns full credit only if NSF International, IAPMO R&T, or WQA certifies the exact model. For every filter, we check the certification listings, the maker’s published data, and what owners report.
What we score
Each filter gets five category scores out of 5. The overall score is their weighted sum, rounded to one decimal place.
| Category | Weight | What it measures |
|---|---|---|
| Contaminant reduction | 40% | What the filter is certified to reduce, under which NSF/ANSI standard, and by which certifier |
| Value for money | 20% | The certified protection you get for the purchase price and replacement filters |
| Filter life and running cost | 15% | How long each filter lasts and what it costs to run, per gallon or per year |
| Ease of setup | 15% | From no-install pitchers to plumbed systems, plus what owners report |
| Flow rate | 10% | How fast it delivers water, from published specs and owner feedback |
For softeners, salt-free conditioners, and iron, sulfur, or manganese systems, whose job isn’t drinking water contaminants, the 40% slot scores treatment performance instead (see below).
Certified, tested, or claimed
A brand can print “reduces lead” on any box. So we sort every claim into one of three kinds of evidence, and label it on every review.
Certified: full credit
NSF International, IAPMO R&T, or WQA certifies the exact filter (and pitcher, where the listing names models) to an NSF/ANSI standard, with factory audits and retesting.
Lab-tested: half credit
A named independent lab tested it to a standard’s method, but no certifier lists it, so there are no audits or retesting.
Claimed: no credit
The maker says so, with no listing or named lab behind it.
We check the listing for the exact model, because claims often differ between versions of the same filter. And we always name the certifier: many filters described as “NSF certified” are certified by IAPMO R&T or WQA. Our guide to NSF certification explains the standards.
How contaminant reduction is scored
Each certified claim adds points, so you can check any score against the listing:
| Certified claim | Points |
|---|---|
| Base: chlorine (NSF/ANSI 42), TDS (NSF/ANSI 58), or any NSF/ANSI 53 health claim, counted once | 2.5 |
| Lead (NSF/ANSI 53 or 58) | +1.0 |
| Total PFAS / PFOA and PFOS only | +0.6 / +0.4 |
| Fluoride | +0.4 |
| Other metals: mercury, cadmium, chromium-6, or copper | +0.2 |
| Arsenic | +0.2 |
| Nitrate | +0.1 |
| Any NSF/ANSI 401 claim, such as microplastics | +0.2 |
- Lab-tested claims earn half the points; maker claims earn none.
- The score is capped at 4.9, and never goes below 1.5, the score for a filter with no certified or lab-tested reduction claim.
- For systems sold in several configurations, we score the claims every standard configuration carries, unless a review names the exact configuration to buy.
Example: the Aquasana Claryum Max Flow is certified by WQA for chlorine (2.5), lead (+1.0), mercury (+0.2), PFOA and PFOS (+0.4), and NSF/ANSI 401 claims (+0.2), for a contaminant score of 4.3. See the under-sink picks.
How treatment systems are scored
For softeners, conditioners, and well water systems, the 40% slot scores the evidence for the system’s main job:
| Evidence | Points |
|---|---|
| Certified by NSF International, IAPMO R&T, or WQA (NSF/ANSI 44 for softeners), or DVGW W 512 for scale prevention | 4.0, plus 0.3 per further certified claim, up to 4.9 |
| Tested by a named independent lab, not certified | 2.0 |
| Maker’s claim only | 1.5 |
The other four scores
Value, running cost, setup, and flow come from the maker’s published specs and prices, replacement filter costs and rated life, and recurring themes in owner reviews. On every review, the score bars show each category so you can see where a filter gains or loses ground. Prices change, so running costs use current filter prices when we update a page.
What owners report
Certifications show what a filter can do in a lab. Owners show how it behaves in a real kitchen, from refill speed to whether filter changes are as easy as promised. On reviews, we summarize recurring themes from buyer reviews, good and bad. We don’t cherry-pick, and we never invent ratings.
How we stay independent
- No brand can pay for a review, a higher score, or a placement.
- When a filter falls short, we say so, however popular the brand.
- We cite the source behind every certification and performance claim.
The site is reader-supported through affiliate commissions, which never change a score. See our affiliate disclosure.
What the scores mean
| Score | What it means |
|---|---|
| 4.5 and above | We’d confidently recommend it to most people in its category. |
| 4.0 to 4.4 | A strong option with a trade-off or two. |
| 3.5 to 3.9 | A reasonable pick for the right buyer. |
| Below 3.5 | Meaningful limits you should know about before buying. |
A high score elsewhere never rescues a filter with weak certified reduction, because that category carries the most weight.
How we choose our picks
Our top pick on every roundup and comparison is the filter with the highest overall score, and the rest are ranked by score. A lower-scored filter can still carry a labelled pick, such as “Certified for Total PFAS”, when the label names a certified claim the higher-scored filters lack. If two filters tie, the one with the higher contaminant reduction score ranks first, and the page says so.
How we keep reviews current
Certifications change, prices move, and rules get updated. We recheck reviews and rankings regularly, and after any major change, such as a new EPA rule or a product gaining or losing a certification. Every page shows when it was last updated.
Think we got something wrong? Email [email protected] and we’ll recheck the listing.