Here’s the core truth: when salt water freezes, the ice crystals that form are almost pure water. Salt molecules are essentially “kicked out” of the ice structure as it solidifies, a process called brine rejection. That’s why icebergs floating in the Arctic Ocean are mostly fresh—you could literally melt one and drink it, assuming you haven’t packed a cocktail umbrella and a sun hat.
But wait—this doesn’t mean you can just toss a bucket of seawater in your freezer and expect fresh cubes. Speed matters. If the water freezes too quickly, impurities, including salt, get trapped in tiny pockets within the ice. Think of it like a snow globe shaken too hard—the salt doesn’t have time to escape the crystal lattice.
For a real-world example, look to sea ice in polar regions. Over months, the ice naturally “drips” out the brine, becoming progressively fresher. Eskimo cultures have known this for millennia, using old sea ice for drinking water. Nature is clever, but your home freezer isn’t a slow-motion Arctic winter.
