A.O. Smith 2-Stage Under Sink Water Filter (AO-US-200)
Listings checked Oct. 16, 2026
Certified to
- NSF/ANSI 42WQA listingchecked Oct. 16, 2026
- NSF/ANSI 53WQA listingchecked Oct. 16, 2026
- NSF/ANSI 401WQA listingchecked Oct. 16, 2026
Certified for: Lead, PFOA, PFOS, Chlorine, Chloramine, Total trihalomethanes (TTHM)
Maker’s list price
$140
as of Oct. 16, 2026
Each replacement, at list price
- 2-stage replacement set (AO-US-200-R)
- $84
Five years, household of 3
$980
18¢ per gallon
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List price from the maker’s site, checked Oct. 16, 2026. Prices change; the maker’s page is the final word.
What the listings say
| Standard | Certifier | Claims | Listing |
|---|---|---|---|
| NSF/ANSI 42 | WQA | Aesthetic Chloramine; Aesthetic Chlorine; Nominal Particulate Class I | Read the listing checked Oct. 16, 2026 |
| NSF/ANSI 53 | WQA | Asbestos; Cyst; Lead; Mercury; Methyl Tert-Butyl Ether (MTBE); Perfluorooctane Sulfonate (PFOS); Perfluorooctanoic Acid (PFOA); Turbidity; VOC (as chloroform) | Read the listing checked Oct. 16, 2026 |
| NSF/ANSI 401 | WQA | Atenolol; Bisphenol A; Carbamazepine; DEET; Estrone; Ibuprofen; Linuron; Meprobamate; Metolachlor; Microplastics; Naproxen; Nonyl Phenol; Phenytoin; TCEP; TCPP; Trimethoprim | Read the listing checked Oct. 16, 2026 |
Certified for, and claimed
Certified, by a listing
Claimed by the maker only
None recorded.
What it costs over five years
Household of 3, 3 gallons a day of drinking and cooking water. Installation not included.
| Item | Replaced | Count | Amount |
|---|---|---|---|
| System, with first media | — | 1 | $140 |
| 2-stage replacement set (AO-US-200-R) | Every 5 monthsgallon rating runs out first | 10 | $840 |
Five-year total$980
Per gallon18¢
Worth knowing
Claims are for the version with its own faucet. A.O. Smith posts MSRPs only and sells through Lowe's, so there is no maker sale price.
Other under-sink carbon filters
- Brondell Coral UC300 Under Sink Water Filtration System42 · 53 · 401
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- Frizzlife SK99 Under Sink Water Filter42 · 53
- Aquasana Claryum 2-Stage (AQ-6200)42 · 53 · 401
- Express Water StreamLine Direct Connect System (USC001)42 · 53 · 401
- LARQ Under Sink Water Filter42 · 53
- Waterdrop 10UA Under Sink Water Filter (WD-10UA)42
- Multipure Aquaversa (MP750)42 · 53 · 401
Where to go next
- Every under-sink filter, rankedBy what their listings cover, then what each costs over five years.The best under-sink water filters, ranked
- Your household’s costThe five-year cost at your own household size and daily use.Run it for your household
- NSF/ANSI 42, decodedWhat a NSF/ANSI 42 listing does and does not promise.About NSF/ANSI 42
- Every filter, checkedSide by side, with what each one can prove.All filters