How Do Water Filters Really Remove Chlorine?


Chlorine is often responsible for your tap water tasting like chemicals or leaving you with a nasty aftertaste. However, chlorine is an essential disinfectant that makes our tap water safe to drink. It is used to treat the water before it reaches our homes and there are many water purification methods we can use in the home to remove the chlorine from our tap water to improve the taste.

Distillation units, faucet-mounted filters, gravity-based water filters, filter pitchers and reverse osmosis systems that use activated carbon filters are able to remove chlorine from water. Chlorine is trapped in the tiny pore spaces of the activated carbon, while the de-chlorinated water is able to flow through.

Not all types of water filtration or purification use activated carbon to treat water, so unfortunately, not all methods are able to remove chlorine. For detailed information on all the methods that can remove chlorine, including home systems, faucet-mounts and refrigerator filters, and how the chlorine is actually removed – see below!

How do water filters remove chlorine? 

First of all, it is important to know that no water filter is 100% effective. That means even if your water filter does remove chlorine, it cannot remove 100% of it. Sorry for the bad news! But many methods remove up to 99%, which is great.

Public Water Systems use chlorine to disinfect our drinking water. Which is great for killing germs, but some chlorine stays in the water and can make it taste and smell funny. So, if you are like me and don’t like the taste of chlorinated water, it is great that water filters and purifiers can actually remove chlorine.

Filters that carry National Sanitation Foundation certification 42 (NSF-42) are able to remove chlorine from water. The NSF says:

NSF-42 Filters are certified to reduce aesthetic impurities such as chlorine and taste/odor.

National Sanitation Foundation

and

NSF-42 Filters can be point-of-use (under the sink, water pitcher, etc.) or point-of-entry (whole house) treatment systems.

National Sanitation Foundation

These 5 methods of filtration and purification remove chlorine and can have NSF-42 certification:

  1. Distillation
  2. Reverse Osmosis
  3. Gravity-based
  4. Faucet-mounted
  5. Filter pitchers

Keep reading to learn how each method is able to remove chlorine:

1. Distillation 

A standard distillation system purifies water by heating and evaporating the water, before cooling the vapor and capturing it for you to drink. This treats water, because it leaves behind all the nasty things that didn’t evaporate, such as bacteria and heavy metals. 

Unfortunately, chlorine evaporates at a lower temperature than water and can survive the distillation process.  

Luckily, there are 2 ways that water distillers can remove chlorine from the distilled water: 

  1. By having two gas vents – one that captures vapors like chlorine, that are lighter than air, and one that safely captures the purified water vapor (although having a distiller with two gas vents is rare)
  2. Using an activated carbon filter after the distillation process

By running distilled water through a carbon filter, as much as 99% of the chlorine can be removed!

2. Reverse Osmosis

All reverse osmosis systems use a semi permeable membrane to remove contaminants from water. Yet, this membrane cannot remove chlorine from water. This is because chlorine is dissolved in the water and the membrane only works on suspended solids.

Luckily though, most reverse osmosis systems should have at least one carbon filter as part of their purification process. Most systems use GAC filters – Granular Activated Carbon, before the water reaches the semi permeable membrane.

This is effective at removing chlorine, and in general is thought to be necessary in reverse osmosis systems, as chlorine can damage the semi permeable membrane.

3. Gravity-based

Most gravity filters use a GAC (Granular Activated Carbon) filter to treat water – which is definitely able to remove chlorine! Some companies that use carbon filters in their counter-top gravity based filters include Propur and Berkey.

But be careful, not all of their products use activated carbon, in fact in some cases they don’t tell you what is in their filters at all!

4. Faucet-mounted

Most faucet-mounted filters use a combination of carbon and mineral (chemical and mechanical filtration) components to filter water.

However, the carbon is not a separate filter, but is combined with the other components. This means some faucet-mounted filters can remove chlorine while others cannot – it depends on the product and brand.

But, many faucet-mounted filters have NSF-42 certification – so you can be sure they remove chlorine. Brands like Brita, Instapur and Pur all have faucet-mounted filters that have NSF-42 certification, and remove chlorine!

Remember to check each product before you buy. Some faucet-mounted filters just say things like ‘reduce chlorine’ but do not provide a % reduction or a statement regarding NSF-42 certification.

5. Filter pitchers

Water filter pitchers that have either a granular or block activated carbon filter are able to remove chlorine. Unfortunately, many filter pitchers do not have these type of filters, instead opting for mechanical or sediment filters that are cheaper. So, be sure to check for NSF-42 certification before you invest in one.

If you are interested in filter pitchers, check out this post I wrote about the 12 things they remove and the 3 things they don’t. You can also check out our resource page for specific information on the only filter pitcher we recommend.

How does activated carbon filters remove chlorine?

Activated carbon filters are very porous, which means they have lots of tiny holes in them. Chlorine, and other organic compounds, get trapped in these tiny pore spaces.

Once the chlorine molecules are trapped in the filter the de-chlorinated water simply flows out the other side of the filter – and tastes and smells much better!

It is extra important to keep up to date with the cleaning and maintenance of your filter. Especially when it comes time to replace your filter cartridges – otherwise your filter is just for show, and chlorine will pass through unimpeded and straight into your glass of water.

What about Chloramine? – can water filters remove it?

Some Public Water Systems use chloramine to disinfect tap water instead of chlorine. Chloramine is much harder than chlorine to remove. However, catalytic carbon is more than capable of removing chloramine – it is similar to activated carbon but has had its electronic structure changed.

Catalytic carbon speeds up the decomposition process of chloramine and effectively filters it out of your water. Even better is the fact that catalytic carbon filters will remove chlorine as well!

Which water filters don’t remove chlorine?

UltraViolet water purifiers are not able to remove chlorine from water. If you still want to use an UltraViolet purification system and get rid of chlorine, you could consider using it with a reverse osmosis system.

Ultrafiltration systems typically cannot remove chlorine, even though they filter out contaminants as small as 0.2microns! On some systems you can choose to have a 0.5 micron carbon block prefilter added before the ultrafiltration process. The carbon block prefilter is able to remove chlorine, and other dissolved contaminants.

And remember, if your filter or purifier doesn’t have NSF-42 certification it isn’t guaranteed to remove chlorine – no matter what the sales pitch says!

Which water filter removes the most chlorine? 

We wish we could recommend a water filter that removes more chlorine than other filters, but we can’t! Almost all water filters use the same method to remove chlorine (activated carbon), so none of them are better than the others.

On the other hand, reverse osmosis systems that use 2 activated carbon filters will remove more chlorine than other filter or purification systems that only use one filter.

Reverse osmosis systems will often have one activated carbon filter before the reverse osmosis membrane, and another one after the membrane. This increases the amount of chlorine the system can capture. Any molecules of chlorine that makes it past the first carbon filter, will most likely be captured in the tiny pore spaces of the second filter.

And don’t forget – water distillers that run distilled water through an activated carbon filter as well are able to remove 99% of the chlorine in your water.

Do refrigerator water filters remove chlorine?

Most refrigerator water filters and icemaker filters use activated carbon to treat water. The activated carbon in the filter is able to remove chlorine, just like other types of home water filters.

Not all filters are created equal though! Watch out for refrigerator filters that only use sediment (mechanical) filters or do not carry NSF-42 certification – these filters will not remove chlorine from your water.

Related Questions 

Why does my filter water taste like chlorine? Water with as little as 1mg/L (or 1ppm, or 0.0000083lb/gal) of chlorine can smell and taste like chlorine. If your filter does not use activated carbon it will not have filtered out the chlorine.

How long does it take for chlorine to evaporate from water? Public Water Systems are required by the EPA to keep chlorine levels below 4ppm (parts per million), or 4mg/L (0.000033lb/gal). 4ppm of chlorine will take around 220hours to evaporate from 10gallons of standing water.

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