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Our Verdict (Best for)
The AO Smith AO-US-200 under sink water filter is easy to set up, use, and maintain, and offers wallet-friendly upfront and long-term costs. We like the fast faucet flow from the sleek, brushed-nickel faucet, and the system’s compact design is both sturdy and space-saving. More importantly, the AO Smith delivered solid results in our lab testing for contaminant reduction, and the filtered water tasted and smelled great. We also have 77 NSF certifications for contaminant reduction, although most are for easier-to-remove organics. One more con: There’s a notable percentage of negative customer feedback on aosmithatlowes.com and lowes.com, whereas Amazon reviews are much more positive (the most common complaint is leaking). Bottom line: A solid but not our favorite under sink water filter.
The AO Smith AO-US-200 is an under sink water filter that requires a plumbing connection and comes with an extra faucet. It’s designed for use as a drinking water filter and can purify both tap water and properly disinfected well water.
As usual, we’ve tested the system with our own hands:
- Hands-on experience: We installed/assembled, used, and maintained it.
- Filtration effectiveness: We sent an unfiltered and a filtered tap water sample to a professional lab for analysis in order to determine real-life contaminant reduction capabilities. Plus, we checked for NSF certifications and other test data.
- More testing: We performed a taste & odor test and a filtration speed test.
- All other product aspects: We considered initial + long-term cost, product warranties, additional features, frequent customer complaints, etc.
Contents
Overall Rating: /5.00
Filtration: /5.00
Usability: /5.00
Costs: /5.00
| Type: | Under Sink Water Filter |
| Price (May 5, 2025, w/o Short-Term Sales): | $139.99 |
| Estimated Yearly Cost (May 5, 2025): | ~$140 |
Overall Rating: /5.00
What We Like Most
- Achieved good results in our lab testing for contaminant reduction.
- Filtered water tasted and smelled perfectly clean.
- Holds NSF certifications for 77 contaminants against standards 42, 53, and 401.
- Easy to set up, prime, and use.
- Fast flow from the dedicated faucet.
- Sturdy, straightforward, and space-saving design, with a nice brushed nickel faucet.
- Easy to maintain with provided filter wrench.
- Filter life indicator.
- Affordable purchase and long-term maintenance costs.
What We Don’t Like
- NSF certifications are mostly limited to “easier-to-remove” organics.
- Notable percentage of negative customer feedback on aosmithatlowes.com and lowes.com. Most common complaint was leaking.
How the AO Smith AO-US-200 Compares to…
18 Other Under Sink Water Filters
In this video, Sara highlights our under sink water filter top picks. The AO Smith AO-US-200 was included in our testing, but didn’t make the cut.
Please note: Our full guide on the best under sink water filters is available here.
Video Chapters + Comparison Sheet
- Link to Comparison Sheet
- 00:00 – Intro
- 00:34 – How We Tested & Rated
- 01:53 – Our Recommendations
- 03:01 – Best Overall (Cloud RO)
- 15:11 – 2 Best Tankless ROs (Waterdrop G3P600 & X12)
- 27:26 – Best Non-RO Filter (Epic Smart Shield)
- 31:22 – Highest Filtration Score (Aquasana SmartFlow)
- 32:02 – Made in USA (USWS All American & Home Master TMHP-L)
- 32:34 – Budget RO Pick (APEC ROES-50 Essence)
- 32:51 – AO Smith AO-US-200 & Culligan US-EZ-4
- 33:34 – Summary
Full Analysis of the AO Smith AO-US-200
Filtration: /5.00
1. Lab Results: /5.00
Remember that our before vs after lab comparison is not an exact science. It’s informational and subject to variability, inaccuracies, and interferences caused by natural fluctuations in water quality, accidental contamination, human error, instrumentation issues, and more. Furthermore, our lab-testing is limited to those contaminants present in our water supplies and at their respective concentrations. As such, it can only give us a general idea for how effective a certain water treatment product might be.
Lab Results Chart
| Potentially Harmful | Aesthetic Issues | Feed Water Level | Filtered Water Level | Reduction Rate | |
| Water Disinfectants | |||||
| Chlorine (mg/L) | ✖ | ✖ | 0.89 | 0 | 100% |
| Disinfection Byproducts | |||||
| Bromodichloromethane (µg/l) | ✖ | 1.81 | 0 | 100% | |
| Bromoform (µg/l) | ✖ | 1.79 | 0 | 100% | |
| Dibromochloromethane (µg/l) | ✖ | 2.75 | 0 | 100% | |
| Chloroform (µg/l) | ✖ | 0.93 | 0 | 100% | |
| Metals | |||||
| Copper (mg/L) | ✖ | ✖ | 0.09 | 0 | 100% |
| Barium (mg/L) | ✖ | 0.04 | 0 | 100% | |
| Boron (mg/L) | ✖ | 0.06 | 0.03 | 50% | |
| Zinc (mg/L) | ✖ | 0.04 | 0 | 100% | |
| Strontium (mg/L) | ✖ | 0.42 | 0.18 | 57% | |
| Salts | |||||
| Nitrate (N) (mg/L) | ✖ | 1.89 | <0.5 | Anywhere Between 74% and 99% | |
| Fluoride (mg/L) | ✖ | 0.58 | 0.57 | 2% | |
| Other | |||||
| Uranium (µg/L) | ✖ | 1 | 0 | 100% | |
| Impurities NOT Detected in Unfiltered Tap Water Sample | |||||
| Explanation: | |||||
| Full Removal | |||||
| Considerable Reduction | |||||
| Concentration More Than Double of Unfiltered Water Sample | |||||
| Potential Leaching Reached or Exceeded the Strictest Public Health Guideline We Could Find | |||||
*100% means reduction to below the minimum detection level. To learn more about our testing procedures check our editorial guidelines.
Link to Filtered Water Report
Link to Unfiltered Water Report
Usability: /5.00
Costs: /5.00
Please note: This page is still a work in progress. Additional content and details will be added shortly – stay tuned!
About the Author(s)
Sara has been a lifelong home-improvement fan (she’s been hooked on This Old House since she was five) and taught herself any project she didn’t already know by watching YouTube tutorials. She is also an award-winning filmmaker. Armed with this skillset, Sara installs, primes, samples, uses, and maintains nearly every point-of-use water treatment systems we test – then brings her results to life on camera for our YouTube channel.
Raoul has a background in mechanical engineering and has been writing about home water treatment since 2015. He designs our product review processes, analyzes the results, and ties everything together. As editor-in-chief, he tries hard to keep the whole operation running smoothly behind the scenes.