If you let water sit out, will the chlorine “evaporate” out of it?
Basically, yes.
It takes well over a month. Check out this thread where I describe an experiment we performed in my lab.
The chlorine will leave. It isn’t quite evaporating - it’s dissolved in the water, and as long as it is less concentrated in the air near the water than it is in the water, more of it will move from the water to the air than from the air back into the water.
I am cheating a little when I say “less concentrated”. It actually has to be less concentrated in a specific sense relating to the fondness chlorine molecules have for mixing with air versus water. When it’s in water this concentration is called “chemical potential”, and when it is in air it is called “fugacity”.
But the point is that chlorine can mix with air or with water, and if you keep fresh air drifting over the water so it can carry chlorine away, eventually it all leaves the water.
I don’t know if this applies to that category. My tap water has a strong chlorine taste, but if I put it in a water jug in the refrigerator (with an open “pour spout” not a tight-fitting lid) it loses that taste in about 24 hours.
My dad would use “aged” tap water for his fish tank. He said basically the same thing: that the chlorine would evaporate out and would then be safe for the fish.
His fish didn’t die with any correlation to his adding water to the tank, so I’d say that it worked.
A lot of the chlorine will leave over a day or two. You can use tap water that’s been sitting out over night or the weekend with no problems in fish tanks (the inhabitants of which are very sensitive to chlorine). Honkeytonk’s experiment was measuring residual chlorine (probly with expensive equipment) as it dissolved from glass jars. Put the water in a pail where there’s some air circulation, and enough will leave that it won’t remain sterile for long.
Oh yeah - tap water has enough chlorine to kill trout, but some hatcheries do run off of city water (if they can afford it). They just run it through an areation tower which in it’s self takes out a lot of the chlorine.
A caution regarding water for aquariums: make sure the water treatment folks in your location aren’t using something other than chlorine. Chloramines take a lot longer than a few days to disappear and will nicely kill off your fish for you.
Don’t mean to hijack, but I would hate for an unsuspecting aquarist to lose a tank or two. However, I agree that if there’s only chlorine “aged” water works just fine, even for sensitive fry, etc. My cat likes it better too. (To drink, not to swim in)
rivulus
My fish loving ex-roomie used to drop a “MillionAir” aerator into a pitcher of water for a few hours, and then use that water to refill his tanks. He said the little bubbles absorbed and removed the chlorine much faster than just sitting around. He had a lot of fish, so . . .
Tris
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