From Liquid to Solid: How Long Does It Take Water to Freeze?

By: Kristen Hall-Geisler & Austin Henderson  | 
instant ice
If left totally undisturbed, a purified water bottle won't freeze until it reaches minus 43.6 degrees Fahrenheit (minus 42 degrees Celsius) and becomes a supercooled liquid. HowStuffWorks

You may have seen videos of what looks like an ordinary bottle of cold water hanging out and minding its own watery business until bam! Someone taps it against the table and the whole bottle turns instantly to ice. What is this dark wizardry?

It isn't magic but instead science that causes the bottled water to completely freeze — and some pretty simple science at that. So, how long does it take water to freeze? Let's find out.


The Mystery of Nucleation

When any substance changes state — like liquid water changing to solid ice — the process involves nucleation. It’s the anchor that creates the first ice crystal and then promotes the rapid formation of more.

Heterogeneous Nucleation

This happens when there are impurities, like dust, present in the water, providing the necessary nucleus for ice formation in water exposed to freezing temperatures. Ice crystals then form throughout the liquid, turning our water into solid ice over time.


Homogeneous Nucleation

Pure water has no impurities, so without a nucleus to kickstart the freezing process, the water becomes supercooled. This allows the water to freeze faster when exposed to an external nucleus, making the magic of "instant" ice possible.


Freezing Point Fun Facts

Water famously becomes completely frozen at 32 degrees Fahrenheit (0 degrees Celsius). But when water is devoid of impurities, like in purified bottled water, the freezing process requires even colder temperatures.

So, if you place bottles of purified water in the cold air of a freezer and leave them a couple of hours, they'll still be liquid because pure water with no nuclei in it freezes at minus 43.6 degrees Fahrenheit (minus 42 degrees Celsius). It's now a supercooled liquid, which does indeed sound super cool.


Let's Make Some Instant Ice!

Ready to freeze water? Grab some water bottles and place them in your freezer. Make sure it's undisturbed for a few hours, getting it to that supercooled state. The exact freezing time? Typically, it takes about two-and-a-half to three hours.

Once the wait is over, remove the bottles with care. Then shake one or whack it on the table.

Anything can act as a nucleus at this point — air bubbles, a slight dent in the bottle. Any little change will be enough to cause homogenous nucleation. Once that disturbance is present, the uniform water molecules will freeze completely and so quickly that it looks instant.


Quick Freezing FAQs and Myth Busting

Which Freezes Faster, Hot or Cold Water?

An interesting phenomenon known as the Mpemba effect suggests that under certain conditions, hot water freezes faster than cold water. Crazy, right?

Do Different Ice Trays Affect the Freezing Process?

Absolutely! A metal ice cube tray, for instance, might speed up the process of freezing water for solid ice cubes compared to a plastic ice tray, because metal ice cube trays conduct heat (and the lack of it). Oversized ice cube trays, on the other hand, might take longer simply due to the larger volume.


What's the Ideal Water for Instant Ice?

Bottled or purified water is typically best for this icy experiment, but tap water, depending on how treated it is, can sometimes work too.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.