Does Reverse Osmosis Remove Chlorine?

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Chlorine is a drinking water contaminant that’s typically added to municipal water before it reaches our homes. It’s used as a disinfectant to remove bacteria and viruses, and keep water free from harmful pathogens as it travels to our homes.

The problem with adding chlorine to water is that, while being helpful in removing contaminants that could cause sickness or disease, the chlorine chemical itself is not fit for human consumption. Early research suggests that chlorine in drinking water may have long-term health effects.

You may wonder, then, why chlorine is still used to disinfect water. The answer is simple: it’s the most cost-effective solution for treatment on a large scale when compared to other means of pathogen removal like UV purification.

It doesn’t look like local authorities will consider using a non-chemical means of water disinfection any time soon, which is why so many at-home chlorine removal methods have cropped up – and reverse osmosis is by far one of the most popular.

🚰 How Does Reverse Osmosis Remove Chlorine?

Does RO filter remove chlorine? The answer is yes! Reverse osmosis filtration systems remove chlorine by sending it through multiple stages of filtration. Typical filters in an RO system are a pre-filter, an activated carbon filter, a reverse osmosis membrane and a post-filter.

If you’ve done any research into chlorine removal at all, you’ll know that activated carbon filters are highly effective at removing chlorine. But reverse osmosis is even more thorough, because after a good majority of chlorine is removed in the activated carbon filter stage, water then flows through the semi-permeable membrane, which has tiny pores that chlorine molecules are too large to pass through.

During RO water filtration, chlorine and the other leftover contaminants are washed away down a drain with wastewater, leaving only pure water to flow out of your faucet.

Closer look of the reverse osmosis membrane

📊 How Much Chlorine Does RO Remove?

Does a reverse osmosis system remove chlorine effectively? Again, the answer is yes – being one of the best methods of water purification, reverse osmosis removes about 98% of chlorine from a municipal water supply. You’ll be left with such tiny trace amounts of chlorine that you shouldn’t be able to test them with a water chlorine test.

🧫 What Other Pollutants a Reverse Osmosis Water Filter Remove?

Reverse osmosis water treatment combines two effective impurity removal solutions – carbon filters and the RO membrane – which enables RO machines to remove virtually all TDS (total dissolved solids) from water, including VOCs (volatile organic compounds), heavy metals like lead, chemical impurities like pesticides and herbicides, and bacteria.

The majority of reverse osmosis membranes are also capable of removing fluoride, a controversial impurity that is added to water by some states for its oral health benefits.

👎 Possible Disadvantages of Reverse Osmosis Systems

Wastes Water

At-home RO units may be best for impurity removal, but a big downside of these units is that they waste water during the reverse osmosis process. Typically, for every 1 gallon of filtered water produced, RO water treatment systems waste around 4 gallons (though newer systems are becoming more efficient).

Healthy Minerals Removed Too

Reverse osmosis water treatment doesn’t focus specifically on removing certain contaminants – it removes them all. Just as the bad impurities are filtered out, so are the “good” – the healthy minerals, like calcium and magnesium, which give water a more appealing alkaline taste.

The only way to remove all contaminants while retaining the good stuff is to purchase a reverse osmosis remineralization filter, or buy your own mineral drops to add to your drinking water afterward.

Maintenance to Keep Up With

You can’t forget about maintenance when you own an RO system, as without regular filter changes, your TDS will rise and the filters will become virtually useless.

Though maintenance isn’t hard, you’ll need to make sure to remember to change each RO water filter stage – usually 3 filters and a semi-permeable membrane – to make sure the system is working at its optimum throughout its lifespan.

The filters generally require changing after 6-12 months, while the RO membrane lasts for 2-3 years.

Can Be Costly

Compared to other water filtration options, reverse osmosis is one of the more expensive upfront purchases.

The best RO filters cost at least $150, and as the pricier units tend to reflect their quality, it’s generally a good idea to make a bigger investment in a unit that’ll last you longer, rather than buying cheap and dealing with issues down the line.

Changing the filters and RO membrane is a long-term cost associated with reverse osmosis filtration units, with filters costing around $45 for a three-pack and the RO membrane costing around $35.

Because you only need to worry about the filters and the RO membrane every year or so, you won’t have to spend hundreds of dollars on replacement filters at once. But it’s still an extra cost to be aware of.

💭 Considerations for Selecting an RO System


It’s best to set a budget before you commit to in-depth research into residential reverse osmosis technology for your household. Some systems are more costly than others, and setting a budget means you can make sure you stick to looking at products that you can reasonably expect to afford.

You don’t have to pay ridiculous prices for a top-of-the-range product that comes with a whole host of extra features (like, for instance, a smart filter change indicator or built-in TDS reader) if you don’t really care either way whether you have these features.

Make sure you buy the technology you can afford – just remember that the cheaper residential RO systems most likely use cheaper materials, which may affect the effectiveness of the RO method of filtration.

System Type

There are two common types of at-home RO system: countertop and under-counter systems.

Using both types of products will reduce or remove a high level of chlorine and chloramines and other dissolved substances in water, and both have a combination of carbon filters, post- and pre-filters, and RO membranes.

The biggest difference is not the RO process, but the design of the unit itself.

Countertop RO units, as the name suggests, sit on a kitchen countertop, where you can get easy access to clean water from the machine itself. Under-sink units, on the other hand, treat water at your waterline before sending it through a dedicated faucet at a kitchen sink for drinking.

When it comes to system design, you will also notice that there are two water storage options: tankless and tank-based.

Many modern RO units are tankless to save space, providing access to a clean water supply immediately.

Tank-based systems, on the other hand, store water in a tank, which then passes straight up to your faucet when you switch it on, saving the time of having to wait a few seconds for the RO process to take place.


Reverse osmosis is incredibly effective, but the way these machines work isn’t the most efficient.

For contaminant-free water to pass through the RO membrane, the contaminants actually have to be removed – and the easiest way to do this is to flush them down a drain line with a small amount of water.

Most reverse osmosis units have a 1:4 wastewater ratio, meaning that they work to remove four gallons of water for every one gallon of impurity-free water produced.

However, you can get RO units with a better wastewater ratio; for example, many units have only 2 or 3 gallons of wasted water for every one gallon of clean water they provide. If you don’t like the idea of water waste, however minimal, there are plenty of more efficient RO units out there.

Related: The most efficient RO system on the market

Water Quality

If you don’t already know your water quality, use a testing kit to learn exactly which molecules have the biggest potential for problems in your water. Aside from chlorine, look out for other chemicals like pesticides, high levels of fluoride, and heavy metals like lead.

Use a TDS meter if you want to measure your water’s total dissolved solids. You can then use this tool again after the reverse osmosis process to see how many contaminants remain after water has been treated. However keep in mind that this will not account for suspended contaminants such as bacteria or sediment.

A good reverse osmosis unit offers a thorough filtration method that can remove the majority of chemicals and organic matter, even offering a fluoride-removal solution.

Related: Our top picks of the best chlorine water filters in 2023

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