Review: AO Smith Under Sink Water Filter (AO-US-200)
Written by: Gene Fitzgerald // Expert Fact-Checking: Buddhini Dolapihilla, MBSS // Last Updated: Sep 12, 2023
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The AO Smith Under Sink Water Filter treats water using two filter stages that combine different types of carbon filter media with ion exchange resin and mechanical filtration. This combination leads to healthier, better-tasting water at home.
The filter also has some impressive NSF certifications, which we’ll look at later in this article.
Keep reading to discover this system’s perks (and downsides).
Contents
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AO Smith AO-US-200 Under Sink Water Filter |
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| Price: | $$ |
| Filter Process: | Activated + Catalytic Carbon, Ion Exchange Resin, Mechanical Filtration |
| Filter Life: | 500 Gallons |
| Flow Rate: | 0.5 Gallons Per Minute |
| Annual Cost: | ~$125 |
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Overall Rating: 4.0/5.0 ⓘRating based on filtration performance, filter life, price and yearly cost, NSF testing/certification, customer support, product warranty, our testing/experience, user feedback, and other factors.
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AO Smith AO-US-200 Under Sink Water Filter – All Specs
- Model: AO-US-200
- Annual Maintenance Cost: ~$125
- Filter Media/Process: Activated Carbon, Catalytic Carbon, Ion Exchange Resin, Mechanical Filtration
- Filter Stages: 2
- Flow Rate: 0.5 gpm
- Filtering Capacity: 500 gal or 6 Months
- WxHxD: 8.25″x9″x4.25″
- Water Temperature: 40-90 °F
- Water Pressure: 20-80 psi
- NSF Certifications: Standards 42, 53, 401
- Warranty: 1 Year Limited
AO Smith AO-US-200 – Key Features
The AO Smith AO-US-200 Under Sink Water Filter consists of two filter cartridges that use four filter stages. These four stages are activated carbon, catalytic carbon, ion exchange resin, and mechanical filtration.
Together they remove sediments, chlorine/chloramine, PFOA and PFOS, microplastics, lead, asbestos, cysts, VOCs, and several other organic and inorganic water contaminants. All in all, this will make your water much safer to consume and also improve its taste and odor.
The filters have a lifespan of 500 gallons (or 6 months). Flow rate is 0.5 gallons per minute (more on this below).
It also comes with a dedicated 100% lead-free, brushed-nickel faucet and a 1-year limited warranty.
AO Smith Under Sink Water Filter Pros
This AO Smith under sink filter system reduces up to 99% of 78 potentially harmful water pollutants. And it is certified of doing so. The AO-US-200 has been awarded with 3 NSF certifications: 42, 53, and 401. In other words, you can be rest assured that it is indeed effective.
Besides, the unit comes with all the parts needed for installation, and there’s no need to shop for extra parts. The system is also pretty easy to install, so there’s no need for a plumber.
Replacement filters are also cheap (only $125 yearly), so the 6-month filter life isn’t a problem really.
What Contaminants Are Being Removed?
The AO Smith AO-US-200 under sink filter reduces up to 99% of 78 harmful contaminants, including:
- 97.3% chlorine
- 97.6% chloramine
- 99.6% particulates
- >99% asbestos
- 99.99% cyst
- 94.1%-99.7 lead
- up to 99.6% mercury
- 95.2% PFOA + PFOS
- >98.9% BPA
- Microplastics
- Dozens of VOCs up to 99%
The AO Smith AO-US-200 – learn more on Amazon.com
Installation
Although there is a dedicated faucet which may require drilling, installing the AO Smith is relatively easy. All required bits and pieces are part of the package so you probably won’t have to call in a plumber.
Please consider these instructions as a general guideline. Always make sure to check and follow your user manual before getting started.
Here are the tools needed to install the system:
- Adjustable wrench
- Measuring tape
- Variable speed drill with 7/32″ bit
- Hammer
- Bucket
- Phillips head screwdriver
Follow these steps to install:
- Shut off your cold water supply and disconnect the water line with an adjustable wrench.
- Fix the brass tee to the shutoff valve and reconnect the cold water line to the brass tee.
- Next, connect the white tube to the brass tee and fix the brass nut onto the tubing (the nut’s threads should face the end of the tube). Then, slide one plastic collar on the tube and place the brass tube insert into the tube’s opening.
- Drive the tip of the tube into the brass tee’s opening and then tighten the brass nut to create a seal.
- Set the faucet rubber washer between the sink and the faucet. Reach under the sink and thread the faucet washer, faucet spacer, and faucet nut onto the tubing. Tighten the nut securely.
- Connect the tubing to the bottom of the faucet. Avoid over-tightening your connections.
- Choose a space under your sink that is at least 12″ away from the base of your cabinet.
- Mark wall screw placements using the mounting holes at the back of the filter unit (the distance between the holes is 2.55″).
- Drill holes for the plastic anchors using a 7/32″ drill bit, and then using a hammer, fit the anchors into the drilled hole.
- Mount the system to the wall using screws and remove the protective plastic strips from the battery compartment. If the battery is installed correctly, the red LED flashes and beeps five times.
- Attach the sumps to the bottom of the filter housing. The sumps should not be on an angle while attaching as it could lead to O-ring damage.
- Fix the tubing from the brass tee into the filter’s inlet side.
- Connect the faucet tubing to the filter’s outlet side.
- Turn on the cold water supply and check for leaks.
The Package (Parts)
- Filter system
- Faucet
- 2x filter cartridge
- Wrench
- 2x 3′ x 1/4″ tubing
- 1/4″ brass tee
- Brass nut
- 2x plastic collar
- Brass tube insert
- Faucet rubber washer
- Faucet spacer
- Faucet washer
- Faucet nut
- Chrome nut
- 2x screws with plastic anchors
- Plastic tube insert
Maintenance
As mentioned earlier, you get around 6 months or 500 gallons of life out of each filter element.
Filter replacements sum up to about $125 a year, which is acceptable.
Here are steps for replacing your filters:
- Shut the cold water valve and depressurize the system by turning on your faucet and letting it run until the water stops.
- Take out both filter housings (to do this, turn each sump to the left and pull it down).
- Unscrew the top of the sumps from the bottom and detach the filter cartridge from the top half of the sump. Dispose of both cartridges.
- Insert the new filter cartridges and reattach the sumps.
- Open the battery door, remove the old battery, and replace it with the new battery (the positive side should be facing the back. If the battery is correctly placed, the system beeps five times and blinks red).
- Turn on the cold water supply and check for leaks.
- Flush the cartridges until the water clears.
Manual
Here is a link to the official manual:
https://www.aosmithatlowes.com/media/1738/ao-us-200_manual_2022_spreads_online.pdf
NSF and Other Certifications
The AO Smith AO-US-200 has been certified against 3 NSF standards:
- NSF 42: For the reduction of aesthetic chlorine, nominal particulate class I, taste and odor
- NSF 53: For asbestos, cyst, lead, mercury, MTBE, perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), turbidity, VOC (as chloroform)
- NSF 401: For atenolol, Bisphenol A, carbamazepine, DEET, estrone, ibuprofen, linuron, meprobamate, metolachlor, microplastics, naproxen, nonyl phenol, phenytoin, TCEP, TCPP, trimethoprim,
Earlier Product Versions
To our knowledge, there are no earlier versions of this product.
AO Smith Under Sink Filter Cons
What are the downsides to this product?
For one, the 0.5 gpm flow rate is a lot lower than what you’d expect from your kitchen faucet. The dedicated faucet is included in this system to mitigate this, but many people may find this flow rate too slow.
The dedicated faucet is also a con on its own; if you don’t have a hole to accommodate it, you’ll have to drill one, which makes installation more difficult.
What’s more, a lot of customers also complained about leaks after changing their filters.
AO Smith AO-US-200 Review: Our Verdict + Best for
The AO Smith is a decent under sink water filter, especially considering the price. Its NSF-certified 2-cartridge system is effective and delivers healthier, better-tasting water due to combination of effective filter media. However, some people may find it too slow due to its low flow rate.
Our Rating in Detail:
- Filtration Performance: 4.0/5.0
- Filter Capacity (Life): 4.0/5.0
- Purchase Price: 4.5/5.0
- Annual Cost: 5.0/5.0
- Overall: 4.0/5.0
Comparison to Other Under Sink Water Filters
Let’s compare the AO Smith AO-US-200 2-Stage Under Sink Water Filter to two other under sink models: The Clearly Filtered 3-Stage and the Epic Smart Shield.
Clearly Filtered 3-Stage |
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| Price: | $$$ |
| Filter Process: | Activated Carbon + Proprietary Blend |
| Filter Capacity: | 2,000 gal |
| Water Flow Rate: | Not Specified |
| Annual Cost: | $440 |
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Overall Rating: 5.0/5.0 ⓘRating based on filtration performance, filter life, price and yearly cost, NSF testing/certification, customer support, product warranty, our testing/experience, user feedback, and other factors.
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Epic Smart Shield |
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| Price: | $ |
| Filter Process: | Activated Carbon Block |
| Filter Capacity: | 651 gal |
| Water Flow Rate: | 1.25 gpm |
| Annual Cost: | $115 |
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Overall Rating: 4.5/5.0 ⓘRating based on filtration performance, filter life, price and yearly cost, NSF testing/certification, customer support, product warranty, our testing/experience, user feedback, and other factors.
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AO Smith AO-US-200 |
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| Price: | $$ |
| Filter Process: | Activated Carbon, Catalytic Carbon, Ion Exchange, Mechanical Filtration |
| Filter Capacity: | 500 gal |
| Water Flow Rate: | 0.5 gpm |
| Annual Cost: | ~$125 |
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Overall Rating: 4.0/5.0 ⓘRating based on filtration performance, filter life, price and yearly cost, NSF testing/certification, customer support, product warranty, our testing/experience, user feedback, and other factors.
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The Clearly Filtered 3-Stage system (see the full review here) also comprises different types of filter media. Its first stage is granular activated carbon, and the second stage contains a “special blend” that captures heavy metals, radiation, VOCs, and PFAS. The third stage is also a secret; what we know is that it binds fluoride and arsenic. Regardless, the Clearly Filtered has really broad filtration capacities. The under sink water filter has been tested against NSF standards 42, 53, and 401 for more than 200 contaminants with excellent results.
Additionally, the system is built in the USA and has a 12-month filter life, limited lifetime warranty, 30-day satisfaction return policy, and an inline design (so no need for an extra faucet).A notable downside is that it’s more pricey to purchase and maintain.
On the other hand, the Epic Smart Shield (check full review) is an inline filter with a single carbon block. It’s NSF-certified to remove chlorine/chloramine, lead, asbestos, cysts, Bisphenol A, VOCs, pharmaceuticals, and more. It’s also NSF-tested against many other contaminants.
The Epic is more affordable to buy and maintain than the AO Smith and the Clearly Filtered system. It also has reliable customer support, a return policy, and a lifetime warranty. You get a reward if you collect 3 filter cartridges and mail them back to the company for recycling. The 1.25 gpm flow rate is lower than the Clearly Filtered’s but higher than the AO Smith’s.
In our opinion, the Clearly Filtered under sink system is the best out of the 3. It’s a premium filter, hence understandably more expensive. The Epic is more affordable in comparison and also highly effective. The AO Smith is a good filter too, but if you don’t want to go through the hassle of installing a dedicated faucet, it’s best to stick with any of the other two filters.
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This completes our review of the AO Smith Under Sink Water Filter. If you have any questions please don’t hesitate to leave a comment below!
About the Author Gene Fitzgerald
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