Tonight a friend told me that pure water does not freeze! He said that a TV show showed a beaker of pure water in a freezer unfrozen, before having a metal rod added and seeing the water immediately freeze. I presume he meant that pure water does not freeze at 0'C, as it must surely freeze at some point. So my question is, can this be true, and also what exactly constitutes pure water anyway? Is it the same as distilled water? If so I have frozen distilled water myself in a domestic freezer.