Review: AO Smith AO-US-RO-4000 Reverse Osmosis System
Written by: Alexandra Uta // Expert Fact-Checking: Buddhini Dolapihilla, MBSS // Last Updated: Jan 29, 2024
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The AO Smith AO-US-RO-4000 Reverse Osmosis System has a couple of promising features, such as solid filtration media, profound NSF testing/certification, and simple DIY-ready installation.
Does that make it the perfect RO system? Find out in this review!
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AO Smith AO-US-RO-4000 Reverse Osmosis System |
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| Price: | $$$ |
| Filter Stages: | 4 |
| Water Flow: | 0.5-0.8 gpm |
| NSF Certifications: | 42, 53, 58, 401, P473 |
| Annual Cost: | ~$220 |
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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-RO-4000 Reverse Osmosis System – All Specs
- Model: AO-US-RO-4000
- Annual Maintenance Cost: ~$220
- Filter Media/Process: Activated Carbon, RO, Activated/Catalytic Carbon + Ion Exchange + Submicron Filtration, Remineralization
- Filter Stages: 4
- Flow Rate: 0.5-0.8 gpm
- Membrane Rating: 35 gpd
- Recovery Rate: 29.43%
- Filtering Capacity: 6-12 Months
- WxHxD: 12″x12.875″x4.25″
- Tank: 3.2 gal
- Weight: 20 lb.
- Water Temperature: 40-100 °F
- Water Pressure: 40-100 psi
- Water pH: 4-10
- NSF Certifications: 42, 53, 58, 401, P473
- Warranty: 2 Years (Limited)
AO Smith AO-US-RO-4000 – Key Features
Let’s start with the “solid filtration media”. The AO Smith AO-US-RO-4000 has four filter stages:
- A carbon pre-filter that reduces chlorine, organics, taste, and smell.
- An RO membrane that blocks most contaminants, including heavy metals like chromium-6 and lead.
- A Claryum filter stage featuring activated carbon, catalytic carbon, ion exchange resin, and submicron filtration. It gets rid of VOCs, pesticides, trace pharmaceuticals, forever chemicals, and many more.
- Lastly, a remineralizer that reinfuses water with healthy minerals like calcium, magnesium, and potassium.
Pretty solid, right? The company says this filter removes up to 99% of 88 dangerous contaminants. We do not doubt that because there are NSF tests and certifications for all 88 contaminants. The system is tested/certified against NSF standards 42, 53, 58, 401, and P473.
Here are some of the reduction rates:
- Chlorine – 96.06%
- Chloramine – 96.06%
- Particulate reduction – 99.9%
- Cyst – 99.95%
- Mercury – 96.6-96.7%
- Lead – 99.3-99.4%
- VOCs – up to 99%
- Asbestos – 99%
- Arsenic 5 – 97.6%
- Chromium 6 – 97%
- Fluoride – 95.7%
- Nitrate/Nitrite – 82.4%
- TDS – 95%
- PFOA/PFOS – 95.8%
All in all, you can expect much cleaner and healthier drinking water using the AO Smith AO-US-RO-4000 Reverse Osmosis System.
What’s more? The brushed nickel faucet that comes with the system is all-metal and completely lead-free.
Filter life: 6-12 months at $220 in estimated annual replacement cost.
AO Smith RO System Pros
Once again, the main thing we appreciate about the AO Smith AO-US-RO-4000 RO System is its effective filtration process, especially because it has NSF certifications backing it. The impressive contaminant rates mean you can be confident about healthy drinking water, and nothing beats peace of mind.
Speaking of peace of mind, you’ll also have that during installation and filter replacements. Both installation and maintenance are DIY-ready.
What if you buy the system and it suddenly develops manufacturing issues? There’s a 2-year limited warranty to take care of that, so no worries.
What Contaminants Are Being Removed?
Here is an almost complete list of contaminants the AO Smith AO-US-RO-4000 removes:
- Chlorine – 96.06%
- Chloramine – 96.06%
- Particulate reduction – 99.9%
- Cyst – 99.95%
- Mercury – 96.6-96.7%
- Lead – 99.3-99.4%
- MTBE – 86.6%
- Turbidity – 99.1%
- VOCs – up to 99%
- Asbestos – 99%
- Arsenic 5 – 97.6%
- Barium – 95.2%
- Cadmium – 95.3%
- Chromium 6 – 97%
- Copper – 96.6%
- Fluoride – 95.7%
- Nitrate/Nitrite – 82.4%
- Radium 226/228 – 80%
- TDS – 95%
- BPA – 98.9%
- Naproxen – 96.4%
- TCPP – 97.8%
- PFOA/PFOS – 95.8%
The AO Smith AO-US-RO-4000 – learn more on Amazon.com
Installation
As mentioned before, this system is DIY-install-ready, so the initial setup is relatively simple. However, the 2-year warranty does not cover issues caused by poor installation, so the company recommends getting professional help. If you have zero plumbing knowledge, you may want to hire a plumber.
Please consider these instructions as a general guideline. Always make sure to check and follow your user manual before getting started.
You’ll need these tools for installation:
- Measuring tape
- Utility knife
- Philips screwdriver
- ⅛” and 7/32” drill bit
- Adjustable wrench
- Protective glasses
- Masking tape
- Bucket
- Regular bleach
And here’s how to install the system:
- Close the cold water supply and open the faucet to drain the pipes.
- Detach the cold water pipe from the shut-off valve.
- Connect the brass tee to the cold water pipe and the shut-off valve. Install the white tubing and other fittings.
- Choose an open area under your kitchen sink to install the system manifold and remineralizer anchor.
- Mark and drill holes for the mounting screws.
- Mount the system manifold and remineralizer holder.
- Drill a 1 ½” hole in your kitchen sink if there’s no existing hole.
- Install the RO faucet and its fittings.
- Install the water storage tank; make sure you don’t over-tighten or cross-thread.
- Connect the ⅜” tubing to the storage tank.
- Pick a spot for the drain outlet and fix the drain connector.
- Install the necessary tubings: brass tee to manifold INLET port, manifold port to remineralizer, remineralizer to RO faucet, manifold to tank, RO faucet to drain connector, and air gap to the membrane drain port.
- Install the carbon and Claryum filters.
- Clean the system with regular bleach and then rinse it thoroughly.
- Open the cold water supply and faucet to remove air bubbles.
- Close the RO faucet and check the system for leaks.
- Once there are no leaks, open the faucet and purge the system for 24 hours.
- After purging, let the tank fill and start using your filter.
Video
The Package (Parts)
- System Manifold
- Filter Sumps + Filter Elements
- Faucet
- Water Storage Tank
- Eyedropper
- Tank Connector
- Plumber’s Tape
- Drain Valve
- Foam Seal
- Flow Restrictor
- Connectors, Elbow, Tee, Nuts, Bolts, Washer, Gasket, Spacer, Screws, etc.
- Tubing
Maintenance
Filter replacements are relatively easy so you can DIY. The filter lives are as follows:
- Carbon and Claryum filters last six months or 365 gallons.
- The other two filters (RO membrane and remineralizer) last 12 months.
Maintenance costs are pretty high, almost double what we’re used to. Plus, we found customers who complained that the filter only lasted two or three months, spiking the already high cost. Customers have also reported terrible leaks after replacing their filters.
Here’s how you replace the filters when due:
- Switch off the cold water valve and open the RO faucet to drain the system.
- Detach the necessary tubing from the filter housing. You press the collar down and gently tug the plug to do this.
- Dispose of the old flow restrictor.
- Turn the sump left and drag it down to remove the cartridge. Throw out the old cartridge.
- Unbox the new cartridge and remove the protective cap on it.
- Fix the cartridge under the top housing. Make sure it sits and locks correctly.
- Connect the new flow restrictor to the red hose and fix it to the drain port elbow.
- Open the cold water line and RO faucet. Allow water to run continuously for 24 hours to purge the system.
- Close the RO faucet and let the tank fill up for two hours. After that, you’re ready to resume using your system!
Manual
Here is a link to the official manual:
https://www.aosmithatlowes.com/media/1340/ao-us-ro-4000_ownersmanual.pdf
NSF and Other Certifications
The AO Smith AO-US-RO-4000 Reverse Osmosis System has earned certifications against five NSF standards: 42, 53, 58, 401, and P473. Here’s what each one stands for:
- NSF 42 covers the removal of chlorine, chloramine, nominal particulate, class 1 particulate, taste, and odor.
- NSF 53 deals with asbestos, cyst, lead, MTBE, VOC, mercury, turbidity, and PFOS/PFOA.
- NSF 58 covers the reduction of arsenic 5, barium, hexavalent chromium, trivalent chromium, copper, fluoride, lead, nitrate/nitrite, radium 226/228, selenium, TDS, turbidity, and cadmium.
- Lastly, NSF 401 means this system reduces atenolol, bisphenol A, carbamazepine, DEET, estrone, ibuprofen, linuron, meprobamate, metolachlor, naproxen, nonylphenol, phenytoin, TCPP, trimethoprim, and TCEP.
Earlier Product Versions
This system has no earlier product versions.
AO Smith 4000 Cons
All good without the bad? Nope. For one, this system has a 29.43% water recovery rate, meaning about 70% of input water goes down the drain. This is common with under sink RO systems that don’t use an internal pump, but that doesn’t make it great. It’s still a lot of water wasted.
Second, this system costs too much to maintain. As mentioned, its replacement filters are about twice as expensive as usual.
We also found complaints (almost too many complaints) about leaking filters and housings. It can be annoying having a unit that constantly makes your kitchen wet.
Some users also complained of a low water flow rate and a shorter filter life than advertised. Some customers said their filters last only two or three months before needing replacement. That’s a lot, considering the already high maintenance cost.
AO Smith AO-US-RO-4000 Review: Our Verdict + Best for
Well, we have an NSF-backed, effective filtration process with high contaminant reduction rates, plenty of tested contaminants, and a fair upfront price — very nice. However, maintenance costs are quite high, and users seem to have many issues using this system (leaks, low flow rate, and low filter life). For now we’re giving it 4 stars.
Our Rating in Detail:
- Filtration Performance: 4.5/5.0
- Filter Capacity (Life): 3.5/5.0
- Purchase Price: 3.5/5.0
- Annual Cost: 4.0/5.0
- Overall: 4.0/5.0
Comparison to Other Reverse Osmosis Systems
The Waterdrop G3 and AquaTru RO systems are two popular options in the market. Let’s see how the AO Smith compares to them.
Waterdrop G3 |
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| Price: | $$$ |
| Filter Stages: | 4 |
| Flow Rate: | 0.42 gpm |
| NSF: | 58, 372 |
| Annually: | ~$145 |
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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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AquaTru |
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| Price: | $$$ |
| Filter Stages: | 4 |
| Water: | 1 Gallon in 10-15 Minutes |
| NSF: | 42, 53, 58, 401, P473 |
| Annually: | ~$100-120 |
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Overall Rating: 4.5/5.0 ⓘRating based on filtration performance, filter life, price and yearly cost, NSF testing/certification, customer support, product warranty, our testing/experience, user feedback, and other factors.
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AO Smith AO-US-RO-4000 |
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| Price: | $$$ |
| Filter Stages: | 4 |
| Flow Rate: | 0.5-0.8 gpm |
| NSF: | 42, 53, 58, 401, P473 |
| Annually: | ~$220 |
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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 AquaTru is the first system we are going to compare, and it’s our favorite. Countertop style, installation-free, space-saving, fast filtration, easy to use – so many reasons to love it. And like the AO Smith, the system has detailed and independent NSF testing and certifications covering almost 80 contaminants. It has five NSF/ANSI certifications (42, 53, 58, 401, and P473), which is quite impressive and guarantees clean water and good health.
AquaTru’s internal pump reduces wastewater to the bare minimum; only 20% or ⅕ of input water gets wasted. It clearly beats AO Smith and the Waterdrop G3 here. The system is made of BPA and BPS-free Tritan plastic, meaning it’s safe and durable.
We didn’t have issues using the system. However, we found complaints about leaks due to design issues. We also learned that some units stopped working after a few months. One more drawback is the higher purchase price (costlier than AO Smith), but thankfully, it’s far cheaper to maintain (about $100-$120 per year).
As for the Waterdrop G3, it is a tankless under sink RO system, meaning it processes water when needed, and there’s no storage tank to take up your space. Like the AO Smith, the system has four filter stages backed with NSF testing/certifications. It has an NSF 58 certification for TDS removal. It has also been tested against NSF standards 42, 53, 58, 401, and P473 for reducing 99% VOCs, 99% chlorine, 98% nitrate, 99% fluoride, 99% arsenic, 99% chromium 6, 99% lead, and 99% PFOA/PFOS.
What’s more? Waterdrop G3 has an internal pump that boosts water pressure such that the system dispenses 0.42 gallons per minute. That means you’ll never run out of purified water, and you can fill a cup in just seconds! It also beats down the wastewater to only 33% of feed water, which is quite outstanding compared to the AO Smith.
Installation and filter replacements are also easy here. The filters last about 550 to 2,200 gallons or 6 to 24 months. But you don’t need to calculate how long you’ve used each filter. The LED lights and sound on the faucet (and RO system) alert you when it’s time for replacement. There’s also a TDS monitoring panel on the faucet and system. The filter replacement process? Very easy. It takes just one turn to remove and change each cartridge. You don’t even need to turn off the feed water, disconnect stuff, or use any tools.
On top of that, you get extra benefits like a BPA-free design, a money-back satisfaction guarantee (full refund if you’re dissatisfied with your unit within the first 30 days), and a 1-year manufacturer warranty (on the condition that you use municipal water). Also, the system costs less to maintain than AO Smith. On the flip side, it is quite expensive to buy. We also found complaints about annoying noises.
Bottom line: If you ask us, the AquaTru is the best choice here. Waterdrop G3 comes second. The AO Smith AO-US-RO-4000 Reverse Osmosis System is also fine, but the constant issues experienced by users make it less of an ideal choice.
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This completes our review of the AO Smith AO-US-RO-4000 Reverse Osmosis System. If you have any questions please don’t hesitate to leave a comment below!
About the Author Alexandra Uta
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