AO Smith RO Filter System for Under Sink Installation AO-US-RO-4000 Tool Reviews by Tool

AO Smith RO Filter System for Under Sink Installation AO-US-RO-4000

AO Smith RO Filter System Offers Pristine Drinking Water with Remineralization

Whole house charcoal water filter systems are great at getting rid of taste and odor in water. When you’re ready to take it to the next level, reverse osmosis takes you there. The problem is that it’s so good at removing particles that it takes out some of the good stuff, too. The AO Smith RO Filter System has something a little special in mind—a remineralization process.

10-Second Summary

  • 4-stage filtration—carbon, RO, Claryum (selective filtration), remineralization
  • Requires a minimum 2-hole sink for kitchen sink installation
  • Includes filter system, water tank, brushed nickel faucet, filters, and all parts required for installation
  • $179 at Lowe’s


AO Smith RO Filter System Key Features

Water Filtering at the Next Level

AO Smith lays claim as the first water filter system to combine three processes—reverse osmosis (RO), advanced selective filtering (Claryum), and remineralization.

The system starts with a carbon filter to remove chlorine taste and odor, mainly. Then it moves onto the reverse osmosis stage.

RO systems do a great job at removing and reducing some of the really nasty chemicals that may have trace levels in your water (even public water systems). Even though your local water regulations determine what safe levels are and regular testing ensures your water is safe, many of us don’t want even trace elements in there. Aside from chlorine, RO can nearly eliminate any remaining lead, mercury, fluoride, and other particles down to 1 micron in size.

After the RO filter, AO Smith adds a Claryum selective filtration system. This is an important step because RO doesn’t remove things like pesticides, herbicides, and VOCs (volatile organics). By the time your water moves through this filter, it’s as clean as it’s going to get.

AO Smith RO Filter System for Under Sink Installation AO-US-RO-4000

There are some things that the system won’t remove. The main ones are iron and micro-organisms, including bacteria (chlorine should kill any micro-organisms before the system removes it).

The downside is that the comprehensiveness of a system like removes some good things, too. So the AO Smith RO Filter System wraps things up with a remineralization process. Among other things, it returns calcium, magnesium, and potassium to your water—elements critical to human body functions.

If you’re checking against National Science Foundation standards, it hit NSF 42, 53, 58, 401 + P473.


When you’re preparing for installation, keep in mind that the brushed nickel faucet that comes with the set isn’t a replacement for your current faucet. The system has a lower flow rate (1/2-gallon per minute) and it needs to ensure hot water doesn’t run through the system (90ºF max).

AO Smith RO Filter System for Under Sink Installation AO-US-RO-4000

You need a two, three, or four-hole sink that gives you access to install that faucet. You might have to give up your soap dispenser or sprayer to make room if you only have a two-hole sink. It’s possible to drill a new 1-1/4″ hole, but be mindful of what material your sink is made of. Some materials are more forgiving than others.

This is going to be a more complex installation than we saw with AO Smith’s whole house filter. If you’re not confident in your plumbing abilities, calling in some professional help might be the best route.


In the Kit

  • AO Smith RO Filter System—carbon, RO, Claryum, remineralizer
  • Filters for each stage
  • Storage tank
  • Brushed nickel faucet
  • All parts required for installation


All filter systems have a useable filter life. Expect to replace the carbon and Claryum filter every 6 months. The RO membrane and remineralizer filters are good for a year.


The AO Smith RO Filter System runs $179 at Lowe’s with everything you need for installation and we’ve seen it on sale for a little less. You can snag the carbon and Claryum filters as a set for $59.98 and replacement RO membrane/remineralizer set for $89.98.

All told, you’re looking at $179 to get started and $60 for your first replacement filters 6 months later. Then it’s roughly $210 per year in filter replacements after that. The system itself has a 2-year warranty.


AO Smith RO Filter System Specifications

  • Model: AO Smith AO-US-RO-4000
  • Household Size: 2 – 3
  • Capacity: 300 gal.
  • Flow Rate: 0.5 (Gallons per minute)
  • Min. Feed Temp: 40° Fahrenheit
  • Max. Feed Temp: 90° Fahrenheit
  • Contaminants Reduced: 88
  • First Stage: Activated Carbon
  • Second Stage: Catalytic Carbon
  • Third Stage: Ion Exchange
  • Fourth Stage: Mechanical Filtration
  • Filtration Strength: Advanced
  • Filter Life: 6 months/12 months
  • Recommended Use: Under Sink
  • Faucet Finish: Brushed Nickel
  • Height: 12.5″
  • Width: 4″
  • Depth: 12″
  • Weight: 20 lbs.
  • Warranty: 2 years limited
  • Price: $179 at Lowe’s
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My r o faucet leaks after 2 months can I get a diagram to replace washers


I just installed the filter a week ago, works great,water tastes great, just low pressure at the tap my guess is the re-mineral filter bottleneck, no big deal, just use it for drinking water and beer brewing, and to top off my fish tanks.


BUYER BEWARE! This system is faulty. It’s been a year and a half and the manifold leaks where the filter sumps attach. AO admitted it was faulty. Sending a new one free of charge because it’s covered under warranty but I have to pay my plumber to now install this again. Also the membrane filter cartridge replacement did not come with the white elbow and had to call company to send one. I was to receive at a certain date. Didn’t receive- had to call again and wait a week for it. I’ve put a lot of money into this… Read more »

Lydia Jenkins

I can’t even get a full glass of water out of it. Is the tank faulty?

David Powell

There is N annoying continuous dripping sound in the drain from the red 3/8 faucet to drain tube.