What Doesn’t Reverse Osmosis Remove? What Do They Remove?

by Jay | Posted on January 20th, 2023

Are you considering using reverse osmosis to purify your drinking water? If so, you’ve come to the right place!

In this blog post, we’ll discuss what reverse osmosis does and doesn’t remove from water — and why that can be important for your health. Let’s dive in!

Technician installing reverse osmosis equipment under the sink close up. Front view. Horizontal composition.

What does reverse osmosis remove?

Reverse osmosis (RO) systems can remove common contaminants from water, including nitrates, pesticides, sulfates, fluoride, bacteria, pharmaceuticals, arsenic, and other heavy metals.

However, there are some contaminants that RO systems do not effectively remove, such as dissolved gases and organic compounds. Additionally, reverse osmosis does not remove dissolved minerals from water, meaning the water will still contain calcium, magnesium, and other minerals. It is important to note that reverse osmosis is not designed to remove bacteria, though it is effective at filtering out most forms of bacteria.

These systems eliminate ions, metals, and certain bacterial, organic, and inorganic pollutants.

Reverse osmosis, in general, can efficiently remove high concentrations of dissolved ions like:

  • Aluminum
  • Cadmium
  • Antimony
  • Arsenic
  • Barium
  • Chromium
  • Beryllium
  • Lead
  • Calcium
  • Chloride
  • Nitrate
  • Copper
  • Selenium
  • Iron
  • Silver
  • Magnesium
  • Sulfate
  • Manganese
  • Mercury
  • Fluoride
  • Potassium
  • Thallium
  • Sodium
  • Thallium
  • Zinc
  • Radionuclides like Uranium and Radium
  • Specific pesticides such as Lindane, Heptachlor, Endrin, and Pentachlorophenol
  • Particles like oocysts, cysts, and asbestos fibers.

What doesn’t reverse osmosis remove?

Reverse osmosis is a powerful filtration process that can remove many common contaminants from water, including nitrates, pesticides, sulfates, fluoride, bacteria, pharmaceuticals, and arsenic. However, some things reverse osmosis systems are not effective at removing from water. Dissolved minerals, such as calcium and magnesium, are not removed by reverse osmosis.

Additionally, reverse osmosis systems cannot remove dissolved gases such as hydrogen sulfide and volatile organic compounds (VOCs). It is also important to note that reverse osmosis does not remove chlorine from water. While reverse osmosis can effectively filter water and make it safer to consume, it is important to understand its limitations.

Reverse osmosis isn’t always the panacea many people think of when it comes to supplying water entirely free of pollutants since certain toxins are molecularly smaller than water.

Common pollutants that can bypass the typical RO filter include:

  • Some dissolved gasses, such as hydrogen sulfide 
  • Some organic substances
  • Radon 
  • Carbon dioxide 
  • Pesticides 
  • Numerous other agricultural treatment items, such as fungicides
  • Herbicides
  • Chlorine: RO systems can remove varying amounts of chlorine, but it’s possible that the typical household RO filter won’t remove all of the chlorine that’s present in water. This filtration will mostly rely on the chemical concentration levels in the water supply.

How does a reverse osmosis system work?

Before forcing water through a semipermeable membrane to eliminate dissolved solids, a reverse osmosis system uses a prefilter to remove sediments from the water.

Before entering a special faucet, drinking water is polished by a postfilter after leaving the RO membrane. Depending on how many pre-filters and post-filters are used, there are different phases in reverse osmosis systems.

Stages of RO system 

A reverse osmosis system’s main component is the RO membrane, but it also has additional filters. There are 3 to 5 filtering stages in a RO system.

There are one or more of the following filters in each type of system:

  • Sediment filter: Reduces contaminants such as rust, dust, and grime
  • Carbon filter: Reduces chlorine, volatile organic compounds (VOCs), and other pollutants that give water an unpleasant taste or odor.
  • A semipermeable membrane: Up to 98% of the total dissolved solids, TDS, are removed by it.


Are reverse osmosis systems effective at removing bacteria?

Reverse Osmosis (RO) is a highly effective water filtration method that can remove many impurities, including bacteria. Although RO is very effective at removing bacteria from water, it is important to note that there are rare circumstances when bacteria contamination is particularly pervasive.

In such cases, RO may not completely remove all of the bacteria. Additionally, RO systems are not designed to remove viruses and other organic compounds, such as chlorine and heavy metals. It is important to consider your individual needs when deciding if RO is the right filtration system for your home.

Does reverse osmosis remove fluoride from water?

Yes, reverse osmosis is an effective way to remove fluoride from water. It uses a semipermeable membrane that allows water molecules to pass through while trapping larger contaminants such as fluoride.

Reverse osmosis removes fluoride from drinking water with a process called membrane separation. Tests of 6 different brands showed that some reverse osmosis filters CAN remove fluoride while others are not as effective. It is important to choose a certified filter for removing fluoride for optimal results.

Can reverse osmosis remove heavy metals from water?

Reverse osmosis is one of the most effective water filtration methods for homeowners. Pressuring water and pushing it through membranes can effectively remove heavy metals such as lead, arsenic, antimony, aluminum, barium, beryllium, and phosphorus from the water.

While reverse osmosis can remove these heavy metals, it cannot remove all contaminants. Dissolved minerals such as calcium, magnesium, and potassium will remain in the water after reverse osmosis filtration. Fortunately, 3-stage filtration systems are less expensive than a 5-stage reverse osmosis system. These systems are also effective at removing heavy metals and other contaminants.

Does reverse osmosis remove chlorine from water?

Reverse osmosis is an effective water purification method that can remove up to 98% chlorine from municipal water supplies. It does not remove chlorine independently but requires an activated charcoal filter for effective chlorine removal.

Reverse osmosis systems are cost-effective and provide plenty of chlorine-free drinking water for households. The Granular Activated Carbon (GAC) filters capture the chlorine, ensuring it does not pass through the reverse osmosis membrane.


Jay is a health and wellness enthusiast with expertise in water quality and nutrition. As a knowledgeable advocate for holistic well-being, Jay successfully manages Type 2 Diabetes through informed lifestyle choices. Committed to sharing reliable and authoritative insights, Jay combines firsthand experience with a passion for enhancing health."