Why Does It Take So Long for Water to Boil?

We’ve all been there: It’s lunchtime, and you’re ready for something hearty! You grab your favorite box of pasta, fill a pot with water, throw a little salt in, place the pot on the stovetop, and fire it up…

And then you wait.

And wait.

Anddddd wait.

What gives? You’ve cranked up the heat as high as it will go! If you’re using a gas stove, you literally have the pot over a flame! You could cook a steak in the time it takes to get the water to start just simmering!

Why does it take so long for water to boil?

Might as well learn something, you have time to spare…

We all know that water boils at 212ºF (if you didn’t before this, you do now). But that’s only half the equation. The other half is a little thing called heat capacity.

If you remember high school physics, you’re aware that temperature technically measures how fast the molecules and atoms of a substance are moving. The faster the molecules move, the hotter the substance. Simple enough.

But to get something hotter, you need to fill it with heat energy, and some things need more energy than others to get their molecules onto the metaphorical dance floor. This is what heat capacity measures. Water, it turns out, has a ridiculously high heat capacity.

The hydrogen in water molecules just doesn’t want to dance. It actively resists being heated up. If water produced the classic 1984 film “Footloose,” it would have twice as many John Lithgows.

Ugh that picture has neither John Lithgow nor boiling water!

Raising the water temperature by even 1ºF takes a lot, and we mean a lot of energy. In contrast, heating up water requires 10 times the energy needed to heat up the same weight of copper, an actual metal. In fact, the only liquid on earth with a higher heat capacity than water is ammonia, but we encourage you not to try this for yourself since ammonia is corrosive both in its liquid and gaseous forms.

Incidentally, heat capacity also explains why the water at the beach always feels so cold, even when it’s 100ºF out.

So, how can you get your water boiling faster? Well, it will take a true feat of culinary engineering so masterful and cunning that…

Oh yeah, right, the lid. Putting the lid on the pot traps the heat that would normally escape from the water into the atmosphere, circulating that energy back in so the liquid heats up faster. While some people say salt helps speed things up, the difference will only be by a few seconds.

Happily, a watched pot with a lid on it will boil, so long as you have the patience!

Reference: Miodownik, Mark. Liquid Rules: The Delightful and Dangerous Substances that Flow Through Our Lives. Boston, Houghton Mifflin Harcourt, 2019.