A.O. Smith AO-US-200
A WQA-certified under-sink filter that is certified to reduce 0 contaminants at about 16.8¢ per gallon.
This listing is the certified replacement cartridge (the part you change on schedule), not a complete installed system. Its certification applies when used in the matching housing or system.
As an Amazon Associate we earn from qualifying purchases — disclosure. Price as of August 20, 2026; check Amazon for the current price.
You want strong contaminant reduction at the kitchen tap without a countertop unit, and are comfortable with a simple under-cabinet install.
Certified to reduce 0 contaminants.
Like most carbon filters, it does not remove fluoride — only reverse osmosis does that.
What is under-sink filter? A carbon-based cartridge (or set of stages) plumbed under your kitchen sink that filters the cold drinking-water line. Compare all filter types →
What it costs to own
| Upfront price | $83.99 |
| Replacement filter (AO-US-200-R) | Find replacement → |
| Estimated yearly cost (filters, ~1.5×/yr) | — |
| True cost per gallon | 16.8¢ |
Cost per gallon and yearly cost are our estimates from the rated capacity and current prices. The filter only works if you replace it on schedule.
Full specifications
| Certified by | WQA |
| NSF/ANSI standards | 42 — reduces taste, odor, and chlorine (aesthetic standard) · 53 — certified for health contaminants such as lead, VOCs, and cysts · 401 — reduces emerging contaminants such as pharmaceuticals and pesticides |
| Filter type | Under-sink filter |
| Rated capacity | 500 gallons |
| Flow rate | 0.5 gpm |
| Replacement element | AO-US-200-R |
| Installation | Mounts under the sink; connects to the cold line. Basic DIY. |
Frequently asked
Is the A.O. Smith AO-US-200 NSF certified?
Yes — the A.O. Smith AO-US-200 is listed in the WQA certified-product database under NSF/ANSI standards 42, 53, 401. That means an independent body verified its claims (not just "tested to" a standard).
What does the A.O. Smith AO-US-200 remove?
It is certified to reduce 0 contaminants: .
How much does the A.O. Smith AO-US-200 cost per gallon?
About 16.8¢ per gallon, based on its rated capacity of 500 gallons and current price.
How often do you replace the under-sink filter?
A under-sink filter like this is typically replaced about 2 time a year (replacement element AO-US-200-R). Replace on schedule — a spent cartridge stops reducing contaminants.
Compare similar under-sink filters
Source: WQA public certification listing. Specs and certified claims are from the official listing; cost figures are our estimates. Some links are affiliate links — see our disclosure.