Does Adding Salt to Water Make It Boil Faster?

When salt enters water, it dissociates into ions and makes it a little harder for water molecules to turn into vapor; this is called boiling-point elevation. The measurement is clear: when one tablespoon (15 ml measure), or about 18 grams of salt, is added to one liter of water, the boiling point rises from 100°C / 212°F to only 100.3°C / 212.5°F. On the stove, that 1/3°C (about 0.6°F) difference amounts to a few seconds, depending on the size of the pot, and cannot be measured reliably with any kitchen timer. So salt does not speed up the water; technically, it slows it down a tiny bit.

The belief comes from a second physical fact, and it is partly right: salt water has a slightly lower heat capacity than pure water, so the same amount of heat raises its temperature a little faster. But this effect works in the opposite direction from the increase in boiling point, and the two largely cancel each other out. The net difference left over is too small to measure under kitchen conditions. What determines how many minutes a pot of water takes to boil is not salt, but the amount of water, the bottom of the pot, and whether the lid is on.

Three things actually help water boil faster. First, putting the lid on: the lid traps the steam escaping from the surface and the heat it carries away, noticeably shortening the boiling time in the same pot. Second, use only as much water as needed; you do not need to fill a pasta pot to the brim—enough to comfortably cover the ingredients is sufficient. Third, match the pot to the burner: in a wide-bottomed pot that extends beyond the burner, the edges heat more slowly than the center, extending the time. A fourth factor is the water’s starting temperature: tap water runs noticeably colder in winter than in summer, so the same pot on the same burner takes a few minutes longer to boil.

The real question about salt is when and how much to add. Salt pasta water after it boils and just before adding the pasta; salt dissolves in boiling water within seconds. The amount is also clear: 7–10 grams of salt for every 1 liter of water, or slightly more than one level 5 ml measure. Use the same ratio when boiling vegetables. Salt only works its way into the food while it is boiling; salt sprinkled on afterward at the table stays on the surface and never gives the same flavor. This also prevents the small pitted marks salt can leave on the bottom of a pot; once the water has fully boiled, adding salt and stirring it in right away leaves it no time to settle on the bottom.