How Long Does it Take for Free Chlorine to Evaporate From Tap Water Entirely?

Surely many aquarists have heard that chlorine will leave facet water after some time.

But exactly how long does it take for tap water with Chlorine to be safe for fish?

Can the clearance be full without the use of chemicals?

What about Chlorine’s cousin – Chloramine.

There are numerous ways on how to remove chloramine from tap water as well, but is evaporation one of them?

Is this an efficient way for dechlorination?

Chlorine is the go-to choice for water facilities because it is cheap and very hostile to bacteria.

It is also rather harmless to humans.

With our friends from EPA regulating things all over the place, we can feel at least a little safe, right?

Maybe.

But what about our fish pets?

Chlorine in tap water is quite toxic to them (some of us have learned that the hard way).

Dechlorinating tap water has become a healthy habit for every fishkeeper out there.

There are times, however, when we can’t really get our hands on them sweet water conditioners.

And we find ourselves wondering…

How long does it take for Chlorine to fully evaporate from tap water?

Depending on its levels of content, the evaporation time for chlorine from tap water can be estimated:

2 ppm of Chlorine will take up to 4 and a half days or around 110 hours to evaporate from 10 gallons of standing water. Ultraviolet light, water circulation, and aeration will speed up the evaporation process dramatically. Chlorine will last between 6 and 8 minutes in 10 gallons of boiling tap water. Boiling is the fastest method to remove Chlorine from water.

Chloramine, however, doesn’t evaporate as quickly.

In fact, it is pretty stable.

It’s why companies use chloramine in the first place.

Chloramine does not gas off as easily and it is more long-lasting.

How long it takes to boil Chlorine and Chloramine out of drinking water?

Boiling water does remove and will clear tap water from Chlorine as heat reduces the ability of water to hold dissolved gas.

Here’s how fast chlorine and chloramine would off-gas when being boiled away:

The evaporation estimate of 1 ppm of Chlorine when boiling 10 gallons of water is just above 3.5 minutes. However, it will take around 60 minutes (1 hour) of boiling to let out all the Chloramine of the same amount of water.

Chlorine VS Chloramine in our tap water?

Why you should care to know the difference:

Free chlorine is being kept in drinking water via pipe pressuring.

As soon as it leaves the sink there is no pressure to hold it inside anymore, and it starts to gas off.

Chloramine, on the other hand, represents the chemical bond between chlorine and ammonia.

Nowadays there’s a good chance that your local authority uses chloramine for water disinfection.

This is the reason behind elevated ammonia levels after dechlorinating with a commercially available water conditioner.

The dechlorinator breaks the bond of chloramine and neutralizes the released chlorine, but the ammonia is still present.

I’ve said this many times, but I guess it’s better to be safe than sorry – always read the label of the products you use in the aquarium.

There are all-in-one solutions commercially available out there, you just need to find them.

Prime, for example, converts chloramine into chloride but takes care of the leftover ammonia as well.

Evaporation times – overview chart

Where I live, the total chloramine content is between 2.7 to 2.9 parts per million.

Being a fan of the scientific approach, I did a couple of tryouts and wrote down my results.

Some additional research showed that Chloramine has around 3.5 times longer time estimate for evaporation than chlorine, depending on temperature and pH levels.

This would mean that if it only takes 1 day for chlorine to evaporate it will take chloramine about 3.

Throwing in additional treatment techniques would change that ratio.

My water was usually around 7.5 – 7.6 pH during the tests.

I did take some measures. Comparing them I acquired some pretty interesting data.

I took the liberty of conjuring a table with estimated chlorine and chloramine evaporation-time periods:

Water treatment	Quantity in Gallons / Liters	1 ppm of free Chlorine	1 ppm of Chloramine
Undisturbed	10 gal / 37.85 liters	up to 55.3 hrs	up to 173.4 hrs
Circulated	10 gal / 37.85 liters	up to 9.6 hrs	up to 70 hrs
Circulated, Aerated	10 gal / 37.85 liters	up to 9.2 hrs	up to 67.6 hrs
Boiling	10 gal / 37.85 liters	up to 3.7 minutes	up to 64.8 minutes

With this chart you can calculate how long would it take for your tap water to become safe for your pet fish, depending on what chemicals your local water facility uses to disinfect it.

It would be wise to call your authorities and ask which one they’re using for disinfection.

I did the tests in my garage to ignore the UV light factor (which, by the way, can be a gamechanger, but more on that below).

Other ways to get rid of the chlorine in tap water:

To naturally dechlorinate tap water try these methods:

1. Campden tablets – I will only mention this because I know it works.

My friend, who’s an avid home beer brewer shared this with me once (Thanks, Em!).

He uses Campden tablets (Sodium or Potassium Metabisulfite) to sterilize the water for brewing.

He swears by it being really effective in removing chlorine AND chloramine.

What did I do? I did my research.

Turns out people did use it to dechlorinate their fish tank water.

So I borrowed some from Em and gave it a go.

It absolutely works, by the way. No ill effect on my fish.

Plus it’s much cheaper than commercial conditioners.

The only catch is that you can purchase the stuff from specialized brewing shops, as far as I’m aware.

I moved away from where Em lived, so I lost my “dealer”.

One of those days, I may look into acquiring some K-meta again…

Anyway, after Em was kind enough to share his dechlorinating adventures with me I became interested in the subject.

Again, I performed heavy research.

Evidently, there’s another way of dechlorinating water.

2. Sodium thiosulfate – it’s the name and destroying all the bad chlorine is the game.

My findings did confirm that commercial facilities use this thing to dechlorinate the water.

However, I never experimented with this one, as people do report high ammonia levels after the treatment.

This leaves the whole “make the water safe for fish” concept behind.

Also, it seems to work with chlorine only, and not chloramine.

I would be happy to hear from you on this one.

Let me know your experience and I will upgrade this article with your report.

3. Moving water – Another useful tip Em gave me about dechlorination is that the more surface area the water has the faster the chlorine will evaporate.

Apparently, chlorine evaporates faster when in contact with air.

Thus recirculating the water will also speed up dechlorination.

Em told me a common old practice where you just move water from one container to another a couple of times.

This gives the water plenty of movement and contact with the air so the chlorine evaporates faster.

If you are okay with looking like a madman you can try it.

I know I wasn’t, so I came up with a workaround. Following this logic, I’ve found that using airstones will speed up dechlorination by almost a half.

One more thing you can do to speed up the process is reaching out to the… sun.

4. Ultraviolet light – Ultraviolet light gives chlorine AND chloramine enough energy to do some mysterious physics and makes them leave the water significantly faster.

I also have two fellow aquarists (one keeps a reef tank and the other – a pond), reporting that leaving a bucket (read 5 gallons) of water sit in the sun for a day would neutralize most Chloramine traces.

Don’t judge them, by the way – every fishkeeper has a moment when they don’t have access to an RO/DI device or a dechlorinator.

Some water facilities do use a method called low-pressure UV dechloramination, so there is merit to their anecdotes.

5. Activated carbon – Lastly, activated carbon filters will definitely get rid of the nasties.

There are such filters in most pitchers and also RO systems.

However, the carbon filters in pitchers will wear out way faster when dealing with chlorine or chloramine.

If you fancy the purifying tank idea, you can set up a filter media like this, to fasten the removal.

RO/DI/Distilled water is your best option.

These purifying methods will get rid not only of chlorines but also everything else that might harm your fish.

If you plan on maintaining a reef tank, proper water purification is a must, as marine life is VERY sensitive to the chemicals in tap water.

Distillation can be costly, but if money is not a factor for you (which I doubt if you’re reading this) then go for it.

Reverse Osmosis and Deionization units that are suitable for coral reef aquariums come at the price of between $80 and $250, but it’s a very cost-effective investment.

They will save you many headaches, not only for dechlorination but also for algae-favoring phosphate levels and whatnot.

It is really the purchase you should be after when you’re done gearing up your saltwater aquarium.

Don’t forget to remineralize after the purification (the link leads to a thorough explanation I wrote on purified water and fish tanks).

Set up your own DIY dechlorinator at home

Following these thoughts, here’s how to remove chlorine from tap water without chemicals at home:

You can set up a “purifying” glass container that sits under the sun with a filter, or perhaps, a wave maker, and an air pump.

This setup may take a day or two of running, but it will eventually get you rid of all the chlorine.

To me, this sounds super expensive just for the sole purpose of dechlorinating, even though the cheapest gear will do the work.

Still, I am obligated to mention it, as I know people that are doing it.

Technically it still counts as evaporation and you’re doing it without any chemicals.

Final Takeaway

Chlorine and chloramine can be removed from the water by off-gassing, but it will take some time.

However, there are many ways to hasten the process and still get the desired results.

You can share how it went for you, and we can have a nice discussion in the comments.

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