Does Chlorine and Fluoride Evaporate from Water?

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Ever poured yourself a glass of tap water straight from the faucet, and noticed that faint smell of chlorine, like a swimming pool.

Then, you sit the glass down for a while and come back to it, and the smell is miraculously gone. What happened?

Chlorine is one of the main things people are looking to get out of their drinking water. The same goes for fluoride.

But is it as easy as just letting them evaporate? Let’s find out.

Key Takeaways

  • Chlorine has the chemical ability to evaporate from water at room temperature, whereas fluoride does not and must be filtered.
  • The time it takes for chlorine to evaporate depends on multiple factors, such as concentration and water temperature.

Do Chlorine and Fluoride Evaporate from Water If You Let It Sit?

Evaporation of something from water requires the compound to turn into a gas at room temperature.

Fluoride is known as a non-volatile mineral, and it does not become gaseous at room temperature. So no, fluoride will not evaporate from water if you let it sit.

Chlorine, on the other hand, does become gaseous at room temperature, so if you let it sit, it will eventually evaporate.

woman sitting in front of water glass

How Long Does It Take Chlorine to Dissipate?

The time it takes chlorine to dissipate depends on the temperature of both the water and the air, and the level of dissolved chlorine in the water. Aeration and circulation can speed up the process.

As a general rule of thumb, let the water sit for around 24 hours. If the component in your water is chloramine, which is used in some places, it will take about 3 times longer.

Standing Water

At an estimate, if there are 2 ppm (parts per million) of chlorine in 10 gallons of water, it will take 110 hours to evaporate.

Moving Water

Water circulation and aeration will speed up the process of chlorine evaporation, but boiling is the fastest method to remove chlorine from water. See the table below for a comparison.

Water Treatment 1 ppm Free Chlorine 1 ppm Chloramine
Standing 10 Gallons 55.3 Hours 173.4 Hours
Circulated 10 Gallons 9.6 Hours 70 Hours
Circulated and Aerated 10 Gallons 9.2 Hours 67.6 Hours
Boiling 10 Gallons 3.7 Minutes 64.8 Minutes

What Are Other Ways to Remove Fluoride and Chlorine from Tap Water?


1. Distillation

This is a process that uses heat to evaporate water. Water is heated until it turns into steam/vapor, and then that vapor is condensed back into liquid water.

It is extremely effective at removing nearly all contaminants and impurities including fluoride. In fact, distillation is considered to create the purest form of drinking water.

2. Reverse Osmosis Water Purification

Pressure forces water through a membrane, that is only permeable to water molecules and other very small molecules. Fluoride is too big to pass through and remains trapped on the other side.

Unfortunately, reverse osmosis alone does not filter chlorine, only a system including another pre-filtration component will do that. Good news is, every RO system on the market features carbon pre-filtration to get rid of chlorine.

3. Activated Alumina Filtration

Activated alumina is a type of aluminum oxide that attracts and binds fluoride ions to its surface. It is capable of removing up to 90% of fluoride from water.

4. Bone Char Carbon Filtration

Exactly what they sound like, bone char filters are made from charred animal bones. The pores of these filters are small enough to trap fluoride on their surface.


1. Activated Carbon Filtration

As mentioned, carbon filtration is the easiest way to remove chlorine from water, and one of the most effective. You can use point-of-use water filtration systems or a point-of-entry water filtration system.

The POE system will provide the entire house with chlorine-free water, which is great if you want to avoid chlorinated shower water as well as drinking water.

Whichever you choose, make sure the system contains an activated carbon filter, which can absorb 99.9% of free chlorine.

2. Distillation/Boiling

One of the easiest and most efficient ways to remove chlorine from your water, as boiling it means the water can no longer hold the dissolved chlorine gas. Depending if your water supply has chlorine or chloramine, the boiling time needed will vary.

Boiling water in a pot

3. UV Light Treatment

Certain UV light water treatment systems can reduce chlorine into by-products by triggering a chemical reaction. You need at least a medium-pressure UV light to be able to do this, or it may not be possible at all.

4. Dechlorination Agent

If you want a relatively fast method to dechlorinate water, you could use a dechlorination agent. There are different chemical dechlorinators available including potassium metabisulfite, sodium thiosulfate, sodium sulfite, and vitamin C.

The time it takes to dechlorinate the water ranges from a few seconds up to 5 minutes. This method can also affect the taste of the water.

Why Are Fluoride and Chlorine Added to Public Water Supplies?

Adding fluoride and chlorine to public water supplies was implemented to improve public health.

  • Chlorine effectively removes viruses, cysts, and bacteria from water, and has been preventing water-borne illness in our communities since the early 1900s.
  • Fluoride was added to help strengthen teeth. It is debated if fluoride is still needed in the water now with advancements in dentistry, and some believe there are better ways to treat water to prevent disease (such as UV water purifiers). Ultimately, it is up to individuals to decide what works best for them in their households.

Health Effects

Chlorine and fluoride have been added to the water supplies to protect public health. Chlorine is an effective treatment for bacteria and viruses that may lurk in your water supply, and fluoride is proven to strengthen teeth and protect oral health.

The amount of both found in municipal water is not high enough to cause toxicity by drinking it.

However, some concerns have been raised about fluoride levels not being able to be well moderated due to it being found in other things, such as toothpaste.

Possible side effects of overconsumption of fluoride include skeletal and dental fluorosis, hypothyroidism, and neurological issues, though nothing has ever been linked to the consumption of tap water alone being the cause.

If you have any thoughts about the question, does chlorine and fluoride evaporate from water, 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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