Plain Talk About Water For Consumers

Updated: July 31, 2006

Indiana Section American Water Works Association

Question: When I put cubes that I've made in my freezer into a glass of water, white stuff appears in glass as the ice cubes melt. What is the white stuff and where does it come from?

Answer: Ice cubes freeze from the outside, so the center of the cube is the last to freeze. Ice is pure water, only H2O, so as the ice cube freezes, all of the dissolved minerals, like the hardness minerals are pushed to the center. Near the end of the freezing, there isn't much water left in the center of the cube, so these minerals become very concentrated, and they form the white stuff the technical name is precipitate. The hardness minerals that cause the white stuff are not toxic. Some commercial ice cubes are cored after they freeze to remove this material. Having posts in your ice cube tray doesn't help as the precipitate must actually be removed by coring.

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