You've probably heard that water turns to ice at 32°F. Here's how it happens. Water, like everything, is made up of tiny molecules. When water gets colder, this makes the water molecules move more slowly. At 32°F, the molecules move very slowly. So, the molecules are able to lock onto one another. Because of this, the molecules form cold, hard ice. If the water gets warm again, the molecules will speed up again, and the ice will melt.