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I've always heard adding salt to water makes it boil faster. Is this true? If so, why? If not, why do people do it?

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    the best way to make water boil faster is to put on a tight fitting lid. Or move to a much higher altitude. which ever is easier.
    – Sam Holder
    Commented Sep 3, 2010 at 9:23
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    @Sam, I would avoid using altitude as a way to speed up boiling (not that it's even easy do). It boils faster because it's at a lower temperature, and for most uses (eg. Tea), the temperature of the water is an important factor, not just the fact that it's boiling.
    – dsample
    Commented Sep 26, 2012 at 13:15

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No. The amount of salt you would have to add to water to make an appreciable difference is enormous.

Salt is added to water for various reasons: to season whatever is being cooked in it; to maintain colour; to maintain structural integrity.

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    And anyway the effect would be the opposite, making it boil slower
    – user2215
    Commented Sep 3, 2010 at 1:52
  • Salt is added mainly to make food taste salty. Salty is better for organism and for taste.
    – Elzo Valugi
    Commented Dec 8, 2010 at 13:42
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    I was under the impression adding salt was specifically to reduce sticking, as with boiling pasta.
    – Zibbobz
    Commented Aug 14, 2014 at 17:12
  • It's a common mistake, mainly because when you add salt in incipient boiling water, this make many bubbles. The reason why of this behaviour is crystalline salt introduces irregularities, that are places where bubbles are born
    – mattia.b89
    Commented Nov 10, 2018 at 16:05
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Actually adding salt to water makes it boil slower; it increases the boiling point so it takes a little longer to get there. It actually doesn't matter what you dissolve in water (or anything else). Adding a dissolved substance elevates the boiling point and lowers the freezing point.

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No. See: http://itotd.com/articles/521/water-freezing-and-boiling-myths/

Anecdotal however, I often observed that if you have water close to the boiling point adding salt can make it boil instantly. Not sure why.

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  • I suspect it is because as the salt is dissolved, that portion of water (salty) is now denser and remains at the bottom of the pan and gets more exposure to the heated bottom. Pure speculation though.
    – Jay
    Commented Sep 3, 2010 at 2:13
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    I would assume the instant boiling is an effect of adding nucleation sites, though this too is speculative.
    – dmckee --- ex-moderator kitten
    Commented Sep 3, 2010 at 2:17
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    @dmckee - I think that is right as well; it isn't that you've suddenly reached the boiling point, you just release a bunch of bubbles of oxygen that are trying to come out of solution.
    – Michael Natkin
    Commented Sep 3, 2010 at 3:20
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    Try this in the microwave: Use a pyrex measuring cup, and nuke a cup of water for about 2 minutes. Watch during the last minute, so that you can time when it starts to boil. Lets assume 1:45. Now, do it again, but only nuke it for 1:40. Take it out, and add a spoonful of salt (Stand back!!!!) It should explode into a boil. What happened is you actually raised the temperature of the water above 100 deg. But the boiling action requires nucleation points (salt crystals!) In the pot on a stove, the bottom is above 100, but the top isn't. Adding salt causes the bottom to nucleate.
    – Chris Cudmore
    Commented Sep 3, 2010 at 15:03
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    Be very careful with the experiment that @chris suggests. Vibrations in the vessel can also nucleate the boiling, and people have been hurt when apparently quiescent liquids suddenly boil over. Ideally you would wear a full face shield, rubber apron and long rubber gloves. (I superheated half a cup of half-and-half and set it off in the middle of the kitchen, once. Splashes went five feet in every direction and the spousal unit and I both got multiple small burns.) That said, this is a fantastic demo.
    – dmckee --- ex-moderator kitten
    Commented Oct 6, 2010 at 19:05
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Some good answers here already, however, there are a couple of small effects to consider:

1) The solubility of gases in water decreases as the temperature is raised. So as you heat water to boiling, the gases dissolved in it become super-saturated. Adding salt to a supersaturated mixture provides nucleation sites for the gas to come out of solution (ie form bubbles). Those bubbles can make the water look cloudy or white, which can be mistaken for the start of boiling.

2) Solid NaCl actually releases heat when it is dissolved in water. Not very much heat, but if the water is on the narrow edge of boiling already, that added heat of dissolution can be enough to get things boiling a half a giffy sooner.

Again, these are both minor effects; the first merely looks a bit like near-boiling, the second probably can't be detected without a good stopwatch.

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    In the table you linked of enthalpies of dissolution, the change in enthalpy for NaCl is positive (+3.87), which means NaCl requires heat to dissolve, rather than releasing heat. In contrast, the change in enthalpy for HCl and NaOH dissolving is negative, and they release heat when they dissolve.
    – DavePhD
    Commented Mar 4, 2021 at 14:08
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    Good golly, you're right. Still, it's a small value.
    – Wayfaring Stranger
    Commented Mar 4, 2021 at 17:35
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I can see why it may be misinterpreted that adding salt makes it boil 'faster'. One thing that the salt WILL do is introduce a surface (on the salt crystal) that helps the dissolved air to release from the water (looks like tiny bubbles). It can lead people to think that this is starting to boil. When water is actually boiling it is because liquid water is turned to water vapor, thus causing bubbles.

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You guys misunderstood. It doesn't make it Faster it makes it Hotter. This will help you understand. http://www.knowswhy.com/why-does-salt-make-water-boil-faster/

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    Interesting point. But how much salt does one need to add to raise the temperature of boiling from 100 to 106 degrees? With sugar, you need 80% sugar concentration to reach 108° to 118° (the first stage given in candy charts).
    – rumtscho ♦
    Commented Apr 17, 2012 at 10:47
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    @rumtscho A lot. van.physics.illinois.edu/qa/listing.php?id=1457 gives ~0.5°C/3% salinity (and says we can scale that). So, 106°C would be around 36% salinity. Except not, as Wikipedia informs me you can't actually do that, 28% is as high as you can go.
    – derobert
    Commented Jan 7, 2013 at 19:05
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I don't claim that it's true, but here's one more explanation, this one in favor of salt making water boil faster: http://www.swri.org/10light/water.htm

Briefly, they say that salt has lower heat capacity than water, and so water+salt will heat up more quickly than water alone. This overshadows the tiny increase in boiling point that the salt will also cause.

On the other hand, that same site says that adding salt to water will increase its volume, where I think the opposite is true (not 100% sure on that one).

Aside: It's fun how such an easy-to-evaluate experiment has so many different opinions, even with regard to the outcome of the experiment, let alone the explanation (:

Here's someone's video of doing the experiment (the water did boil faster with salt): https://www.youtube.com/watch?v=qcrDuc-XjRQ

Of course, you can poke plenty of holes in their methodology. We need a large government-funded study!

Here is one more link relating to the specific heat of water, when substances are dissolved in it: physics.stackexchange.com There, they did an experiment on cooling water, and found that water+salt cools faster. I think it's reasonable to believe that it heats faster, too.

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It would increase boiling speed by being a bubble nucleator. We are talking kinetics not thermodynamics. The slight boiling point elevation would make little difference.

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Salt decreases the vapor pressure within the vessel of whatever you're trying to boil. Therefore more pressure is needed to overcome the atmospheric pressure and for your liquid to reach a boil.

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its because a lot of households have hard water which has many ions and a high boiling point. adding NaCl softens water and actually reduces ion content in the tap water making it easier to boil. everyone else is theoretically right to state that adding table salt to water increases boiling point but that is for pure water not tap water.

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    How does dissolving an ionic substance in it reduce ion content? Is it making something precipitate out?
    – Peter Taylor
    Commented Jan 28, 2012 at 10:18
  • Salt doesn't soften water. "Hard" water has calcium and magnesium compounds dissolved in it. They will still be dissolved in the water after adding salt, so adding the salt hasn't altered the hardness.
    – David Richerby
    Commented Aug 14, 2014 at 18:28
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The salt in the water is denser so it goes down on the bottom and it takes a lonnnnnnggggg time for the water to boil but on the other hand, no salted water boils water faster!

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