Does Reverse Osmosis Remove Fluoride and Chlorine?

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Reverse osmosis systems are one of the most popular water filtration systems currently on the market.

They are designed to remove up to 99.9% of contaminants including heavy metals, salts, and chemicals.

Two of the main impurities that people want to remove from their water are chlorine and fluoride. Does reverse osmosis remove them? And how does it work exactly? Let us break it down for you.

Key Takeaways

  • Reverse osmosis itself does not remove chlorine from water, but it does remove fluoride. The extra components found in most reverse osmosis systems are what remove the chlorine.
  • Reverse osmosis systems usually remove chlorine by filtering it through activated carbon before it reaches the RO membrane. The RO membrane will then remove the fluoride.

Does Reverse Osmosis Remove Fluoride and Chlorine from Water?

For fluoride removal, RO systems are a great choice. So yes, the process of reverse osmosis removes fluoride from water very effectively (usually around 95%).

However, reverse osmosis itself does not remove chlorine. Good news is, all reverse osmosis systems for home use come with other components that do remove chlorine (usually more than 95%) – think carbon filters.

How Does Reverse Osmosis Remove Fluoride and Chlorine?

The leading reverse osmosis systems have at least 4 or 5 stages of filtration. These usually include;

  • Sediment pre-filter(s)
  • Carbon pre-filter(s)
  • The RO membrane
  • Carbon post-filter

These individual filter stages are designed to remove multiple contaminants from your water supply. In case of chlorine, the water disinfectant is removed by the carbon pre and post-filters.

Under Sink Reverse Osmosis System

As mentioned earlier, the semipermeable reverse osmosis membrane does not remove chlorine. In fact, it rather sensitive to it and might get damaged when getting in contact with chlorinated water. That’s why RO systems feature carbon pre-filters in the first place. They remove most of the chlorine before the water reaches the RO membrane.

How Reverse Osmosis Works

Fluoride, in contrast, is removed by RO membranes. How?

Reverse osmosis systems have been engineered based on the principle of osmosis – which basically means if you have two water solutions with dissolved salts, separated by a semipermeable membrane, the solvent will always flow from the low to the high concentrated side due to osmotic pressure. This will continue until both salt concentrations on either side are even.

In reverse osmosis, the opposite happens, and water molecules move from the side with a high concentration of solvent (the feed water) to a low concentration of solvent (drinking water). So, the process separates the water from the solutes to produce pure drinking water.

How RO Systems Work

The additional pre-filters in an RO system treat the water before it gets to the membrane, getting rid of chemicals like chlorine among other stuff.

Then, high pressure forces the water through the RO membrane, leaving all remaining contaminants behind. Wastewater with these contaminants is collected and then disposed of through a drain line.

The semi-permeable RO membrane contains millions of tiny pores, as small as 0.0001 microns in size. This is large enough to allow H20 to flow through, but almost nothing else.

The Effect of Chlorine on Reverse Osmosis Membranes

As stated earlier, a reverse osmosis membrane alone is not suitable for filtering chlorine. In fact, chlorine can damage it. All RO water filtration systems, for this reason, will have at least one pre-filtration stage to get rid of the chlorine before the water reaches the membrane.

How Much Fluoride Does Reverse Osmosis Remove?

This varies. On average, they can remove 85-95%. This is likely due to the quality of the RO membrane that is used. The AquaTru reverse osmosis system, for example, removes 93.5% fluoride, while the Aquasana OptimH2O removes 95.7%.

How Much Chlorine Does Reverse Osmosis Remove?

Reverse osmosis itself removes none, but the other components of the water filtration system will, depending on what model you get. Every unit with at least one carbon filter is capable of removing up to 95% and more.

Do All Reverse Osmosis Systems Remove Chlorine/Fluoride?

Every single one we tested has at least one carbon filter, so yes. Just make sure that the system you purchase has adequate pre and post-filters included in it, to make sure you are filtering out both chlorine and fluoride, and not causing damage to your RO membrane.

What Else Does Reverse Osmosis Remove?

Reverse osmosis systems are capable of removing a multitude of harmful substances from your source water, such as:

  • Chlorine and chloramine
  • Lead
  • Chromium 6
  • Cadmium
  • Arsenic
  • Fluoride
  • Radium
  • Sulfate
  • Nitrate and nitrite
  • Phosphorous
  • Pesticides
  • Pharmaceuticals
  • Volatile organic compounds (VOCs)

What Is Not Removed By Reverse Osmosis?

Contaminants that are capable of getting through an RO membrane are:

  • Pesticides
  • Herbicides
  • Fungicides
  • Some dissolved gasses
  • Certain organic compounds
  • Chlorine

Farmer Spraying Pesticides on Wheat Field

Pros and Cons of RO Water Purification

Effective Contaminant Reduction

An RO system can remove hundreds of impurities due to its multi-filter process and semipermeable membrane which its tiny pores.

Improved Water Aesthetics

Water is generally clearer, and the flavor of chlorine and other trace chemicals is eliminated.

Easy to Install and Use

RO systems are easy to install, and the different filter elements last between 6 months and 2-3 years before needing to be replaced.

Water Wastage

This is one of the bigger cons. The systems can waste up to 4 gallons of water for every gallon they purify.

Loss of Healthy Minerals

When an RO system filters out all the bad stuff, it, unfortunately, filters out all the good minerals too. This can be combated by adding a remineralization component.

Considerations When Buying an RO System

System Type

  • Point-of-use filters – these are located either on the counter or under the sink and only treat the water coming out of that particular faucet.
  • Whole house RO systems – point-of-entry water filters treat all water that comes into your household.

NSF Testing and Certifications

Always look for NSF/ANSI certifications before buying. This will ensure your system is effective and made with high-quality materials.

Filter Process

Make sure the additional filtration components meet your requirements. Have your water tested to make sure the system will target what you need it to.

Water Demand, Pressure & Wastage

If your water pressure is less than 40 psi, you will need to purchase an RO system with an inbuilt pressure pump.

Some produce up to 4 gallons of wastewater for every gallon purified. Others much less, which is important to take into account when thinking about your level of water usage.

Installation + Maintenance

Consider a reverse osmosis filter that is DIY, which will save you a lot of money.


Consider the initial price tag and annual maintenance cost before deciding if a system is right for you.

Is Chlorine and Fluoride in Water Safe to Drink?

A safe amount of chlorine in water is a maximum of 4 ppm, which is usually well above the levels found in municipal water. The benefits of chlorine treatment in water supplies are thought to outweigh the risks.

Fluoridation in water supplies in the US does not exceed 1 ppm, which is not remotely high enough to cause fluoride toxicity, which is usually only seen after the consumption of high quantities of solute fluoride salt from fluoride-based pesticides.

young woman drinking water

However, some of the health concerns raised in recent days range from skin issues to cancer concerns, none of which have been proven as caused by drinking city water.

If you have any thoughts about the question, does reverse osmosis remove chlorine and fluoride, please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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