The same broad Affinity filtration as Clearly Filtered’s popular pitcher, plumbed onto your cold-water line for on-demand water instead of a slow pour. It targets 232+ contaminants and keeps your minerals. The honest catch is cost: it is expensive to buy and one of the priciest systems to run that we cover.
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The pitcher’s filtration, plumbed in and priced accordingly
The Clearly Filtered 3-Stage Under the Sink puts the same Affinity filtration as the brand’s popular pitcher onto your plumbing. It connects inline to your cold-water line and runs through your existing kitchen faucet, so there is no separate faucet to fit and no drilling, and you get filtered water on demand instead of waiting on a slow pitcher pour.
It targets a big list, 232+ contaminants, and because it is not reverse osmosis it keeps beneficial minerals and wastes no water. On paper that is an appealing combination: broad removal, plumbed-in convenience, and mineral-rich taste.
The honest framing is the same as the pitcher: tested, not fully certified. Independent, accredited labs have tested it to NSF/ANSI methods (42, 53, 401, 473) across that long list, with strong headline results, up to 99.81% PFOA/PFOS, 83 to 99% fluoride, plus lead and chlorine. But as a system it holds only NSF 42 certification, for chlorine, taste, and odor; the health claims are lab-tested rather than NSF-certified, and independent testing found a few contaminants, such as nitrate, only partly reduced.
The cost is the story. Expect around $500 to buy it and roughly $400 a year in replacement filters, more than double what most systems cost to run. The pitcher gives you the same filtration for a fraction of the price if you can live without the plumbed-in convenience.
How it scored, category by category
Each category is weighted into the overall score. Broad filtration and easy, mineral-keeping installation are its strengths. The high upfront price, steep filter cost, and only-moderate flow are what land it a hair below the cheaper pitcher.
What it removes
The Affinity media is genuinely broad, and strongest on the contaminants people buy this filter for. We report the tested-versus-certified distinction honestly, and note where independent testing was less impressive.
| Contaminant | Result | Basis |
|---|---|---|
| Chlorine, taste & odor | Near-complete | NSF 42 certified |
| PFAS (PFOA / PFOS) | Up to 99.81% | Lab-tested, not certified |
| Fluoride | 83–99% | Lab-tested, not certified |
| Lead & heavy metals | Reduced | Lab-tested, not certified |
| Disinfection byproducts, uranium | ~100% | Lab-tested, not certified |
| Nitrate, boron, strontium | Partial | Lower in testing |
| Calcium & magnesium | Kept | Not RO |
As a system it carries NSF 42 certification (chlorine, taste, odor). Its wider claims, fluoride, lead, PFAS, and the rest of the 232+ list, are third-party tested to NSF/ANSI methods by accredited labs, not NSF-certified as a finished system. We credit certified performance and the strong lab results, and flag the contaminants that tested lower. For independently certified health-claim reduction, our top pick, the AquaTru Carafe, is IAPMO-certified to NSF/ANSI 53 and 58. See our fluoride guide and PFAS guide.
Pros and cons
What we liked
- Broad Affinity filtration: fluoride, PFAS, lead, and 232+ contaminants targeted
- Keeps beneficial minerals and wastes no water, unlike reverse osmosis
- Uses your existing faucet: no separate faucet, no drilling, quick DIY install
- On-demand filtered water, no slow pitcher pour to wait on
Worth considering
- Expensive: ~$500 upfront and around $400 a year in replacement filters
- Only NSF 42 certified as a system; health claims are lab-tested, not certified
- Flow is moderate (~1 GPM); some owners report low water pressure
- The pitcher delivers the same water for a fraction of the cost
What actual owners report
Our score reflects certified performance and independent lab testing. Owner sentiment, summarized from verified buyer and independent long-term reviews, is positive on the water and the taste, with cost and flow the sticking points.
Owners like the clean, mineral-rich taste and the convenience of filtered water straight from the tap. The two recurring complaints are how much the filters cost to replace and, for some, weaker water pressure than they expected.
Owners consistently praise
- Clean taste with minerals kept in, water available on demand
- Simple inline install using the existing faucet, no plumber
- Confidence in the broad, independently tested contaminant list
Common complaints
- Replacement filters are expensive and add up fast
- Water flow and pressure can feel weaker than a normal tap
- High upfront price for a non-certified, non-RO system
Qualitative summary of recurring themes across verified buyer and independent long-term reviews, current as of August 2026. We report the patterns we see, positive and negative, and never cherry-pick.
The details
Common questions
Is the Clearly Filtered under-sink NSF certified?
As a system it carries one NSF certification, Standard 42, which covers chlorine, taste, and odor. Its broader claims, fluoride, lead, PFAS, and the rest of the 232+ contaminant list, are third-party tested to NSF/ANSI methods (53, 401, 473) by accredited labs, but not NSF-certified as a finished system. The lab results are genuinely strong, so we credit them, but if an independent, system-level certification for those health claims matters to you, a reverse-osmosis system like the AquaTru Carafe is IAPMO-certified to NSF/ANSI 53 and 58.
Is it better than the Clearly Filtered pitcher?
It uses the same Affinity filtration, so the water quality is essentially the same. The under-sink’s advantage is convenience: it plumbs into your cold-water line and delivers filtered water on demand through your existing faucet, with no slow pouring. The downside is cost, it is far more expensive to buy and roughly $400 a year to run, versus around $165 for the pitcher. If you want the filtration and can live with pouring, the pitcher is much better value.
Does it remove fluoride and PFAS?
Yes, both are among its strongest results in independent testing: up to about 99.81% for PFOA/PFOS and roughly 83 to 99% for fluoride, along with lead, chlorine, and disinfection byproducts. Just remember these are lab-tested figures rather than NSF-certified ones, and testing found some other contaminants, such as nitrate, only partly reduced. See our fluoride guide and PFAS guide for the certified alternatives.
How hard is it to install and maintain?
Installation is straightforward: it connects inline to your 3/8-inch cold-water line and uses your existing faucet, so there is no drilling or separate faucet, and most people finish in about 15 minutes. Maintenance is just periodic filter changes, roughly once a year at 2,000 gallons, but that is where the cost lands, at around $400 a year for the filter set. There is no filter-change indicator, so you track it yourself.
Should you buy it?
Buy the Clearly Filtered 3-Stage Under the Sink if you love the broad Affinity filtration but want it plumbed in for on-demand water rather than a slow pitcher pour, and you value keeping your minerals with no wastewater. On what it targets, it is one of the broadest carbon-based systems we cover.
Go in clear-eyed about two things. As a system it is only NSF-certified for chlorine and taste, with the fluoride, lead, and PFAS numbers lab-tested rather than certified. And it is genuinely expensive, both the roughly $500 upfront and the roughly $400 a year in filters.
If you want the same filtration for far less, the Clearly Filtered pitcher is the value pick. If you want independently certified health-claim reduction, a reverse-osmosis system like the AquaTru Carafe or the certified Aquasana OptimH2O gives you certified fluoride and lead removal. But for plumbed-in, mineral-keeping, broad-spectrum carbon filtration, the 3-Stage delivers. Compare it in our best under-sink filters guide.