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Most municipal water supplies in the U.S. include noticeable levels of chlorine or chloramine added to kill microbes, and often adds an objectionable chemical smell.

Does chlorine evaporate when cooking? If so, does it require boiling temperatures? Does it become more concentrated if the water is boiled down? Does it matter when water is added as an ingredient, such as in bread dough?

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This doesn't seem to be cooking related to me, so OT. Could you edit this to be more relevant? – GdD Mar 2 at 15:36
I don't follow your line of thought. Please elaborate. – Jeff Axelrod Mar 2 at 15:47
I personally think this is fine as is. – Jay Mar 2 at 16:03
@GdD It's the smell that's the cooking-related part. I've never lived anywhere with enough chlorine in the water to notice it, but I guess if your tap water smells like a swimming pool it'd be an issue. – Jefromi Mar 2 at 20:46
Houston and Chicago water absolutely smell like swimming pools if unfiltered. – Jeff Axelrod Mar 2 at 21:32
up vote 15 down vote accepted

Water treatment often uses chlorine or chloramine to kill germs or algae. If you are smelling it it's more likely to be Chloramine than Chlorine. Chlorine will dissipate from water over time naturally, but boiling for 20 minute will drive it out. Chloramine will also dissipate naturally, but in a much longer time frame, and would take over a day to boil out.

So boiling water will get rid of chlorine but not chloramine (at least not in a useful time frame), and boiling will concentrate other minerals in the water which is usually undesirable. It will also de-oxygenate the water, making it flat. Flat water isn't great for cooking - compare the flavor of a cup of tea or coffee brewed with flat water as opposed to fresh and you'll see what I mean.

Your best option for water treatment chemical removal at home is an activated charcoal filter unless you want to invest in a UV treatment system, which would seem to be a bit OTT. You could also use a reducing agent from a brewery supply company, but if all you want is some fresh tasting and smelling water then the filter is your best option.

Homebrewing SE has a thread on this which is worth reading.

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If you look at the solubility curves for chlorine (or other gases) in water, you'll see that just bringing the water to the boil drives off the gas. You don't need to hold it at boiling point. – Chris H Mar 2 at 19:50
Have you actually tried the coffee/tea thing? Heating water to close to its boiling point essentially drives off all dissolved gases so regardless of whether water is "flat" before you made tea or coffee with it, it's flat by the time you're brewing. – David Richerby Mar 2 at 21:25
@DavidRicherby I'm also sceptical, perhaps this merits a separate question? – Lilienthal Mar 2 at 21:59
@ChrisH: It's not an instant thing. Keep in mind that water has a very significant surface tension. All the chlorine that no longer is dissolved forms bubbles which initially aren't even microscopic. IOW, that chlorine isn't dissolved, but still physically located within the fluid. As the water boild, steam bubbles form and fluid currents become significant, causing chlorine bubbles to merge and be carried off. – MSalters Mar 3 at 12:10

If your are dealing with chloramine, a trick I've used in homebrewing is to add powdered ascorbic acid (vitamin c) while heating the water up to around 170 for 15 minutes or so. This will pull the chloramine out of solution and you'll end up with some particulate solid residue on the bottom of the pot from the reaction, so you'd probably want to decant the water off of it to use for cooking. I have been told that it also works for chlorine, but my tap water uses chloramine so I've never tried it for that.

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170F I assume, not 170C (which would be pressurized). Makes sense, though. Ascorbic acid is a well-known anti-oxidant which actually means it's preferentially oxidized, and chlorine is a strong oxidizer. – MSalters Mar 3 at 12:10

You can use as ascorbic acid to remove chlorine and chloramine. The cheapest and most useful form is called Ball brand fruit fresh powder found in all canning supply aisles. It is a fantastic product to use as a substitute for citrus juice to prevent browning and is completely tasteless. Benefit is you get a megadose of vitamin C!

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What happens to the chlorine/chloramine? It must still be there in some form... and since you say the ascorbic acid is tasteless, presumably you aren't convering up the taste. – Jefromi Mar 20 at 1:05

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