A. O. Smith · Under-sink reverse osmosis
A. O. Smith RO with Microbial Boost AO-US-RO-MB-4000: what it removes and what it costs
Model: AO-US-RO-MB-4000 (Lowe's exclusive); filters AO-US-RO-MB-R, AO-US-RO-MEM
The A. O. Smith RO with Microbial Boost AO-US-RO-MB-4000 is certified (NSF/ANSI 58, NSF/ANSI 53, NSF/ANSI 42 and NSF/ANSI 401) to reduce PFAS (PFOA/PFOS), lead, chlorine, chloramine, fluoride and arsenic and 6 more of the contaminants we track. For 2 people drinking and cooking with it, replacement filters cost about $270 a year; A. O. Smith doesn't publish how much it sends to the drain.
12
certified reductions we track
37¢
filters per gallon at rated life
Price checked 2026-10-23. We may earn a commission.
What the A. O. Smith RO with Microbial Boost AO-US-RO-MB-4000 removes
"Certified" means a certifier (NSF, WQA, IAPMO or CSA) lists this exact product for that reduction claim; the listing is linked. "Brand test only" means A. O. Smith cites a lab report but no certifier lists the claim. See certified vs. tested.
| Contaminant | Status | Evidence |
|---|---|---|
| PFAS | Certified | IAPMO R&T listing, NSF/ANSI 53 ("PFOA/PFOS") |
| Lead | Certified | IAPMO R&T listing, NSF/ANSI 58 ("Lead") |
| Chlorine | Certified | IAPMO R&T listing, NSF/ANSI 42 ("Chlorine") |
| Chloramine | Certified | IAPMO R&T listing, NSF/ANSI 42 ("Chloramine") |
| Fluoride | Certified | IAPMO R&T listing, NSF/ANSI 58 ("Fluoride") |
| Arsenic | Certified | IAPMO R&T listing, NSF/ANSI 58 ("Arsenic (Pentavalent) <=50 ppb") |
| Chromium 6 | Certified | IAPMO R&T listing, NSF/ANSI 58 ("Chromium (Hexavalent)") |
| Mercury | Certified | IAPMO R&T listing, NSF/ANSI 53 ("Mercury") |
| Cysts | Certified | IAPMO R&T listing, NSF/ANSI 58 ("Cyst") |
| VOCs | Certified | IAPMO R&T listing, NSF/ANSI 53 ("VOC") |
| TDS | Certified | IAPMO R&T listing, NSF/ANSI 58 ("TDS") |
| Copper | Certified | IAPMO R&T listing, NSF/ANSI 58 ("Copper") |
Not verified, either way (no certification or brand claim): Nitrate, Microplastics, Bacteria and viruses, Iron, Uranium, 1,4-dioxane.
What it costs to run
Yearly cost = replacements per year × filter price, for each filter it uses; a filter is replaced at its gallon rating or its month limit, whichever comes first, plus the water sent to the drain at an average water and sewer price. Water use: drinking and cooking water (0.28 gallons per person a day, EPA's average adult intake).
| Household | Gallons a year | Filters a year | Drain water | Total a year | Per gallon |
|---|---|---|---|---|---|
| 1 person | 102 | $270 | ratio not published | $270 | 264¢ |
| 2 people | 204 | $270 | ratio not published | $270 | 132¢ |
| 4 people | 409 | $270 | ratio not published | $270 | 66¢ |
Per-gallon costs in the table are for real use, so they also count drain water and any filter replaced at its month limit before it reaches its gallon rating. At rated filter life alone, filters cost 37¢ a gallon (the figure at the top of this page).
Rated production is 11.64 gallons a day; 2 people need about 0.56 — well within it. Colder water and lower pressure reduce actual output.
Replacement filters
| Filter | Rated life (gallons) | Rated life (months) | Price |
|---|---|---|---|
| AO-US-RO-MB-R Claryum, carbon and microbial remineralizer set | 365 Source note | 6 Source note | $99.99 Source noteMSRP on aosmith.com aosmith.com |
| AO-US-RO-MEM RO membrane | 730 Source note | 12 Source noteaosmith.com: every 730 gal or 12 months; Lowe's brand page says every 2 years aosmith.com | $69.99 Source noteMSRP on aosmith.com aosmith.com |
Specs
- Type
- Under-sink reverse osmosis
- Price
- —
Source note
Sold only through Lowe's (item 960789); A. O. Smith brand page (aosmithatlowes.com) lists no price or MSRP aosmithatlowes.com
- Installation
- DIY (under-sink or inline fittings)
- Rated production
- 11.64 gallons per day
Source note
IAPMO NSF/ANSI 58 daily production rate (test conditions); brand states no nominal GPD myplc.iapmo.org
- Flow rate
- 0.8 gal/min
Source note
IAPMO listing 0.8 gpm; brand spec table says 0.5 gpm myplc.iapmo.org
- Needs power
- No
- Remineralization
- Yes
Compare the A. O. Smith RO with Microbial Boost AO-US-RO-MB-4000
Updates about the A. O. Smith RO with Microbial Boost AO-US-RO-MB-4000
- August 3, 2026 · EPA publishes protocol for its fluoride toxicity review
Common questions
What does the A. O. Smith RO with Microbial Boost AO-US-RO-MB-4000 remove?
The A. O. Smith RO with Microbial Boost AO-US-RO-MB-4000 is certified (NSF/ANSI 58, NSF/ANSI 53, NSF/ANSI 42 and NSF/ANSI 401) to reduce PFAS (PFOA/PFOS), lead, chlorine, chloramine, fluoride and arsenic and 6 more of the contaminants we track. For 2 people drinking and cooking with it, replacement filters cost about $270 a year; A. O. Smith doesn't publish how much it sends to the drain.
Does the A. O. Smith RO with Microbial Boost AO-US-RO-MB-4000 remove PFAS?
Yes. It is certified for PFOA/PFOS reduction under NSF/ANSI 53 (IAPMO R&T listing).
How much does the A. O. Smith RO with Microbial Boost AO-US-RO-MB-4000 cost to run?
About $270 a year for 2 people ($270 for 1, $270 for 4), counting replacement filters and the water sent to the drain, for drinking and cooking water (0.28 gallons per person a day, EPA's average adult intake).
Data checked 2026-10-23. 102 filters tracked.