What Is Reverse Osmosis and How Do RO Systems Work?

Learn everything you need to know about reverse osmosis and how RO systems work to provide healthier, better-tasting tap water.

By: Maggie Pace

Reverse osmosis is considered one of, if not the most effective water filtration methods to remove contaminants. The technology has advanced significantly as water filters have become increasingly popular, and consumers can now have a variety of RO systems to choose from when picking one for their home, business, or anywhere that can benefit from better tap water. 

Before you start looking at systems, it’s a good idea to understand the reverse osmosis process and how RO filters work. Not all RO systems offer the same features and performance, so having some basic knowledge can go a long way in helping you find the right solution. In this guide, we’ll cover everything you need to know including what reverse osmosis is, how RO systems work, filtration stages, and more helpful information to keep in mind when shopping around.

What is reverse osmosis?

Reverse osmosis (RO) is a water filtration process that removes contaminants by pushing water through a semi-permeable membrane at a high pressure. As water is pushed through the membrane, contaminants get caught and are left behind so only filtered water can pass through. In this sense, the semi-permeable acts as a screen to catch impurities like sediment, chemicals, and metal particles.

How do reverse osmosis systems work?

Reverse osmosis systems remove contaminants by forcing unfiltered water through a semi-permeable membrane at a high pressure, which leaves contaminants behind. RO systems often have multiple stages of filtration to remove additional contaminants throughout the process.

Reverse osmosis system filtration stages

Although reverse osmosis is a powerful filtration method on its own, the process won’t remove all contaminants which is why most RO systems use 3-4 stages of filtration.

Sediment Filter

The sediment filter is a pre-filtration step that catches large particles of dissolved solids such as dirt and debris. Without a sediment filter, these particles can damage the delicate reverse osmosis membrane.

Carbon Filter

RO systems utilize a carbon filter to remove organic chemicals like herbicides and pesticides.

Reverse Osmosis Membrane

The reverse osmosis membrane is what allows RO systems to harness the power of this filtration process. Water is forced through the semi-permeable membrane at a high pressure so that only filtered water can pass through. The process is more effective than microfiltration, ultrafiltration, and nanofiltration — it will only allow particles of 0.0001um to pass through.


Reverse osmosis is so effective at removing particles, that in addition to contaminants, it also frequently removes minerals that are actually healthy for your body such as calcium, potassium, and magnesium. To restore the healthy minerals in water, some RO systems utilize remineralization technology which also improves th pH balance and alkalinity for an improved taste. In Aquasana’s reverse osmosis system this technology is known as Claryum®. Not all systems feature remineralization technology, so check before buying if this is important to you.

What do reverse osmosis systems remove?

The process of reverse osmosis will remove all organic compounds, viruses, and most minerals. It will not remove chemicals such as chloramines, VOCs, PFOS, and PFOA. To remove these contaminants, reverse osmosis systems will use other methods which is why systems often feature multiple stages of filtration.

"... we highly recommend opting for a system that has remineralization technology."

Do I need a reverse osmosis system?

Reverse osmosis is a powerful filtration method that RO systems can utilize to help improve the safety and quality of tap water in your home, business, or anywhere else yous see fit. 

Whether you need a reverse osmosis system or not is dependent on the contaminants that are currently present in your water. You can request a local water quality report to find out what’s in your water and if you need a filter. If the contaminants concern you, look at different types of water filters such as whole house, under sink, and countertop systems to determine which option is best for your home. You may find that a less powerful filter will handle the job, but you can always choose to use an RO system if you want extra peace of mind. 

If you choose to go the RO route, we highly recommend opting for a system that has remineralization technology. Without it, the RO system may remove healthy minerals that also improve the taste of tap water. If you aren’t sure where to start, check out our OptimH2O® Reverse Osmosis + Claryum® system that featured remineralization technology along with exceptional performance. In fact, our system is tested and proven to remove 5x more contaminants than other reverse osmosis systems. Find out more about this system and how it can help you enjoy healthier, better tasting tap water!


OptimH2O® Reverse Osmosis + Claryum®

Combines Claryum® and reverse osmosis technology to remove 88 contaminants including fluoride and arsenic.