When you watch a cooking show on TV, you get evenly divided advice to either add or not add salt to water because it will affect the boiling speed. Those on the side of adding salt contend that it will speed up the process to add the salt, while those telling you not to add say it will slow down boiling. So, will adding salt to water speed the time which it takes the water to boil?
This myth is confirmed! Adding a small amount of salt to a pot of boiling water will generally take some time, up to about 1 minute, off the time it takes to boil.
Now for the science: When water boils, the bonds that hold the 2 hydrogen molecules to the one oxygen molecule begin to loosen because of the heat. Eventually, enough heat (212°F) loosens the bonds so that the water boils. When salt is added it changes how the molecules move in the pot, making them move faster, which produces more heat. Because you are now heating the pot of water on the stove AND the salt is causing the molecules to move, the by-product of which is heat, the water in your pot will boil slightly faster. Basically, adding salt reduces the temperature at which water will boil – meaning you have to add less heat from your stove because the way the salt makes the water molecules move adds heat too.
Remember that the salt in the water will alter the taste of the food you cook in it, so take that into consideration as you try this at home.