Aquasana OptimH2O Under Sink Reverse Osmosis System Review 2023

Author: Rory Mullan - Published: 2021/06/30 - Updated: 2023/01/05

Disclaimer: This page may contain affiliate links. If you buy a product or service through an affiliate link, we may earn a commission but at no additional cost to you. You can view our full affiliate disclosure here.

This product review features the Aquasana OptimH2O Under Sink Reverse Osmosis System.

Reverse osmosis filtration systems are one of the most effective filters that can remove up to 99% of contaminants including microorganisms from your water. The dilemma? They purify the good elements too. Don’t worry; we think we found the solution!

Our search for the safest RO system has led us to the Aquasana OptimH2O under sink reverse osmosis system, which features a bonus remineralization stage. It removes all the bad boys, then adds the good ones back, resulting in evidently clean water.

Want to know more about the Aquasana OptimH2O water filtration system, the pricing, and maintenance? Find out here!

Let’s begin by discussing why the Aquasana OptimH2O is one of the top water filters around. Then, we shall also do a quick overview of the four stages in the filtration system that purify, polish, and replenish your drinking water.

Aquasana OptimH2O Reverse Osmosis System Review – Main Specs

Aquasana OptimH2O Reverse Osmosis + Claryum System


See More Product Images at

  • Filter stages: 4
  • Flow rate: 0.5 gallons per minute
  • Maximum provided filtered water volume: 13.32 gallons per day
  • Recovery rate: 20%
  • Estimated filter replacement cost per year: $200
  • NSF: 42, 53, 58, 401, P473
  • Operating pressure: ‎40-100 psi
  • System dimensions: ‎12×4.5×12.5 inches
  • Tank dimensions: ‎16×11 inches


At the beginning of our Aquasana OptimH2O reverse osmosis system review, a few highlights:

4-Stage Filtration: How Does It Work?

To begin with, the four-stage filtration ensures that your water is crystal clear and free from numerous harmful contaminants. Here is how it works.

  • Activated carbon filter: The first stage reduces chlorine and other chemicals causing bad taste and odor. Sediments are removed, too. Consequently, the subsequent filters don’t clog with big particles.
  • Reverse osmosis membrane: Here, the water is purified from nitrates, nitrites, lead, and arsenic, plus many other harmful contaminants.
  • Claryum carbon: At this stage, the system eliminates pesticides, herbicides, chloramine, heavy metals, and industrial contaminants. This is possible because the mixture of activated plus catalytic carbon is really powerful.
  • Remineralization: This is where the water gets back all the essential minerals to become wholesome again. The water returns to a balanced pH level thanks to the influx of calcium, magnesium, and potassium.

Extensive NSF Certifications

We are greatly impressed by the NSF/ANSI certifications and protocols that back every claim by the manufacturer. The unit is certified to NSF 42, 53, 58, 401 coupled with confirmation to NSF protocol P473.

Many companies fail to go through such intensive certifications and ultimately lose consumer trust. However, the Aquasana guarantees up to 99% removal of 88 harmful water contaminants. Safe to say, Aquasana takes its filtration and certifications very seriously.

To demonstrate, here is what each NSF certification depicts.

  • NSF 42: It tests the filter’s performance relating to chlorine and other odor-causing elements.
  • NSF 53: It checks the filter’s ability to remove contaminants posing a health threat.
  • NSF 401: Measures the system’s performance relating to industrial runoff chemicals, herbicides, pesticides, and detergents.
  • NSF 58: This certification is especially administered for water filters that utilize reverse osmosis purification at the point of use. It measures the unit’s capacity to remove Total Dissolved Solids.
  • Protocol P473: It focuses on the removal of PFOA and PFOS which are known carcinogens.[1]

Effortless Installation & Maintenance

This is perfect for do-it-yourselfers.

90-Day Refund Policy

You can make use of the 90-day refund policy if you are not happy with how the RO system performs.


  • The Aquasana RO water filter is relatively effortless to install and maintain. Since you don’t require professional help, you save a lot of cash on yearly replacements.
  • The faucet comes in three metal finishes, bronze, nickel, and chrome. So, you can select the required design depending on other fittings in your kitchen.
  • We love that the system includes a 2-year limited warranty. As a result, you don’t incur additional costs in case of malfunctioning.
  • In case the unit isn’t up to your expectations, you can demand a full refund within 90 days, no questions asked.
  • While it may not sound ideal, the system purifies and wastes water at a ratio of 1:4. To clarify, for each gallon filtered, four gallons go down the drain. This is the standard ratio for most RO systems.
  • The system filters 0.5 gallons of water per minute, and the daily filtration capacity is around 13.32 gallons. Both are sufficient for regular home use.


Although we are pretty convinced of the quality, we have noticed a few concerns that we would like to address.

  • Some customers have reported that the under sink water filter is not as sturdy as expected. In particular, the quality of the faucet is relatively moderate. We understand that the system focuses more on water filtration and less on fittings.
  • We have also read about leakages in the filter system. Thankfully, Aquasana support team is quick to send replacements free of charge.


Installing the Aquasana OptimH2O is not exactly a piece of cake. However, if you have a basic idea of plumbing around the house and are not intimidated by DIY, you can attempt the installation yourself.

Moreover, all components required for the setup are included in the package, and clear instructions are laid out in the manual. Here’s a summary:

  1. Prior to starting the installation, close the cold water supply and turn on the kitchen faucet to release pressure and drain all water.
  2. Installing the brass tee fitting
    1. Disconnect the cold water line from your existing kitchen faucet.
    2. Install brass tee on cold water line and attach ¼” white tubing, compression nut, plastic sleeve, and brass insert.
  3. Installing RO system module
    1. Mounting the unit is optional. Choose an area with at least 4-inch clearance below the RO system to allow for comfortable filter changes.
  4. Installing the storage tank
    1. Wrap plumber’s tape around top nipple on the tank (clockwise).
    2. Install the tank connector onto the nipple.
    3. Cut and install ⅜” tubing to the tank.
  5. Install the RO dispenser
    1. Drill 1”hole in sink top or use existing hole.
    2. Place the rubber gasket into faucet groove.
    3. Feed all tubing and threads through hole in countertop.
    4. Secure the faucet from underneath using the washer, spacer, and nut.
    5. Add quick connector to faucet base.
    6. Attach ⅜” tubing to quick connector.
  6. Establishing drain line connection
    1. Install drain connector on sink drain pipe. Secure with nuts and screws.
  7. Connecting the tubing
    1. Connect all tubing pushing it all the way in to prevent leaking.
    2. Connect brass tee – manifold, manifold – remineralizer, remineralizer – faucet, manifold – tank, air gap – RO membrane, faucet – drain connector.
    3. Cut excess tubing to prevent kinds etc.
  8. Installing the filter cartridges
    1. When installing the different filter stages, make sure any connections points are aligned. The filters need to be pushed into the manifold and turned right until locking in place.
  9. Sanitizing
    1. Disconnect tubing from manifold outlet leading to the tank.
    2. Add bleach into the tubing at the tank end.
    3. Reconnect the tubing.
  10. Pressure test
    1. Open the water supply.
    2. Open kitchen faucet to purge any air.
    3. Close kitchen faucet and RO dispenser.
    4. Within the next 2 hours, check all connections for leaks.
  11. Purging
    1. Open the RO faucet for 24 hours. This will flush out any installation debris and prime the different filter media.

Finally, you can consult the video available online for a comprehensive explanation of the installation procedure.


With quick-connect fittings and easily accessible filter cartridges, the Aquasana is nothing but effortless to maintain. On the whole, it isn’t a pain to replace the filters since Aquasana designed the reverse osmosis system specifically keeping the ease of use in mind.

Moving on to another critical factor: the cost of replacement filters. According to our estimate, the system costs around $200 yearly in replacement filters. Obviously, this amount depends on your household size, water consumption, and, most importantly, water quality.

If you are interested in saving filter costs, subscribe to the Water for Life replacement filter program. With this in mind, here is when you need to replace your filters.

  • Carbon pre-filter: Bi-annually or 365 gallons
  • RO membrane: Minimum one year to maximum three years
  • Claryum filter: Bi-annually or 365 gallons
  • Remineralization filter: Once a year

What’s Included

Here is a list of the parts included in your package. It consists of all fittings that you need to set up the unit.

Filter System

  • RO module with filter and membrane housings
  • RO membrane
  • Carbon filter
  • Claryum filter
  • Remineralizer


  • Water storage tank (3.2 gallons)
  • Stand
  • Connector


  • One faucet in your selected finish with connector

Additional Parts

  • Plumber’s tape
  • Brass tee
  • Drain saddle
  • 90° elbow
  • Color-coded tubing
  • Flow restrictor

Aquasana OptimH2O Review – Conclusion & Best For

The Aquasana OptimH2O has the edge over other reverse osmosis systems. It’s best for effective filtration – think extensive NSF certifications – and remineralization.

While there are some negatives, such as the rate of water wastage, we accept it at the expense of out-and-out filtration. To sum up, we love the Aquasana OptimoH2O RO water filter system due to its performance and fair price.

If you have questions about our Aquasana reverse osmosis review please leave a comment below!

Further Reading


Meet Rory Mullan

Rory Mullan Rory has joined the Water Masterz team as a contributing writer. He has covered all sorts of topics in the last several years.

Outside of his writing work, Rory enjoys photographing the Irish landscape and making music!

Leave a Reply

Your email address will not be published. Required fields are marked *

18 − 10 =