Some wizard knows why this happens.

[pitzerwm]

http://www.sootoday.com/content/news/full_story.asp?StoryNumber=50683

 

[mac]

Although I'm not really a wizard, I can sort of explain it. It's referred to as supercooled water. Under just the right circumstances water will cool well below the freezing point. It needs to be pretty clean water and usually undisturbed. Pilots have experienced this for years while flying through rain at high altitude. When the water hits the plane, instant ice. It has brought down many aircraft. This bottled water is most likely close to spot free, i.e. below 30 ppm in TDS. And it's just sitting outside. Now if we could only explain how a galss just washed in hot water and sat inverted on a bar, will float around on it.

 

[mjwalsh]

Hmmm----- that was minus 4 Fahrenheit --- I wonder if there is a broad range of below freezing temperatures where this phenomenon will occur?

 

[ted mcmeekin]

intuitive? maybe not

http://www.phys.unsw.edu.au/~jw/unfreezable.html