Photo of an undersink with an RO water filter

Reverse Osmosis Water Filters: How Do They Work?

Introduction to Reverse Osmosis Water Filters

Drinking water that's pure, clean, and devoid of harmful contaminants is no less than a boon in today's polluted world. That's where Reverse Osmosis (RO) water filters come into the picture as a popular choice among households. Have you ever found yourself wondering about the science that backs this powerful method of water filtration? Well, strap in as we uncover the fascinating process of reverse osmosis!

Diagram of water flowing through the RO filtration stages.

Image by macrovector on Freepik

What is Reverse Osmosis?

Reverse Osmosis, in its essence, is a water purification process. This process leverages a partially permeable membrane to sift out impurities from water. By applying pressure on the side of the water containing impurities, water molecules are coerced through the membrane, leaving the unwelcome contaminants behind. This leaves you with pure water on the other side.

Components of a Reverse Osmosis Water Filter

The RO water filter isn't a mere standalone device; it's an assembly of various components working in harmony. Understanding these components is the first step to deciphering how RO filters work.


As the first line of defense, pre-filters work to protect the RO membrane from damage. They remove larger contaminants like sediment and chlorine that could otherwise clog or degrade the membrane. The sediment filter catches dirt, dust, and silt, while the carbon filter ensnares chlorine and other harmful substances that affect the membrane's integrity and life.

Reverse Osmosis Membrane

The reverse osmosis membrane is the heart and soul of the RO system. It's responsible for tackling dissolved impurities, from salts and metals to bacteria and viruses. The membrane pores, measuring a tiny 0.0001 microns, allow only water molecules to pass, ensuring an incredibly high removal rate of up to 99% of the dissolved contaminants.


Once the water has been through the rough ride of purification, post-filters give it a finishing touch. They further remove any lingering tastes and odors, thereby enhancing the aesthetic appeal of the purified water. This ensures that the water you receive is not just pure but also palatable.

The Process of Reverse Osmosis

Understanding the various stages of the RO filtration process can provide a clear picture of how this powerful filtration method works.

Stage One: Pre-Filtration

The first stage, also known as pre-filtration, is where the water first comes in contact with the filtration system. The water passes through pre-filters which remove larger contaminants like sediments and chlorine. These filters essentially serve as the 'bodyguards' for the RO membrane, protecting it from damage caused by these larger contaminants.

Stage Two: Reverse Osmosis

Next comes the actual reverse osmosis stage. Here, water is forced under pressure through the semipermeable RO membrane. This membrane effectively removes a vast majority of smaller, dissolved contaminants that managed to get past the pre-filters.

Stage Three: Post-Filtration

The final stage, post-filtration, polishes off the process. At this stage, water flows through the post-filter or a set of post-filters. This further refines the water by removing any remaining tastes and odors, making it crisp, clean, and delicious.

Pre-filters and post-filters of an RO system.

Image by macrovector on Freepik

Benefits of Using Reverse Osmosis Water Filters

The benefits of RO water filters are manifold. Not only do they significantly improve the taste of water by removing impurities, but they also play a crucial role in your health by reducing potentially harmful substances. Some of these substances include lead, arsenic, and other heavy metals, nitrates, nitrites, and more. Moreover, they are capable of removing disease-causing pathogens, offering you an additional layer of protection against waterborne diseases.

Limitations and Considerations

Despite their benefits, it's also important to acknowledge the limitations of RO systems. For instance, they produce a significant amount of wastewater - for every gallon of purified water, up to 3-5 gallons of water goes waste. Also, RO systems remove beneficial minerals from the water, which some people may find unfavorable. However, many modern RO systems come with a remineralization stage to add these healthy minerals back.

How to Choose the Best Reverse Osmosis Water Filter

When you're in the market for an RO system, consider factors like filtration capability (does it remove the contaminants in your water?), size (do you have the space to install it?), price (does it fit within your budget?), and maintenance requirements (are you comfortable with the maintenance it needs?).

Maintaining Your Reverse Osmosis Water Filter

Maintenance is key to ensuring the longevity and efficiency of your RO system. This includes regularly changing the filters as per the manufacturer's instructions, cleaning the system to prevent buildup, and periodically checking the system for any leaks or malfunctions.

Conclusion: The Value of Reverse Osmosis Water Filters

In conclusion, RO systems provide a comprehensive solution for water purification. They offer you an easy and effective way to ensure the water you and your family consume is safe, clean, and of high quality. Despite some limitations, the benefits and peace of mind that RO systems offer make them a worthwhile investment for your health and well-being.

Image of a family enjoying clean water from an RO filter.

Image by Freepik

Frequently Asked Questions

How often should I change my RO filters?

Typically, pre- and post-filters should be changed every 6-12 months, while the RO membrane should be replaced every 2-3 years. However, this can vary based on your system and water usage.

Does RO water need to be remineralized?

RO systems do remove beneficial minerals from the water. Some people choose to use a remineralization filter to add these back into the water, but this is a matter of personal preference.

How much water does an RO system waste?

An RO system can waste 3-5 gallons of water for every gallon it purifies. However, modern systems with efficiency features can reduce this number significantly.

Can I install an RO system myself?

While it's possible to install an RO system yourself, it can be a complex process. If you're not comfortable with DIY, it's best to hire a professional for installation.

Is RO water safe to drink?

Yes, RO water is safe to drink. It has been purified and stripped of harmful contaminants, making it safer than unfiltered tap water in many cases.

Featured Image by macrovector on Freepik

Back to blog

Related Articles