Oe thing that helps water turn into ice is bacteria! Watch how it takes just a second for Pseudomonas syringae to turn a whole jar of water into ice in this video after the jump.

It works in the same way how snow forms inthe atmosphere. an ice crystal needs to form around a nucleus and it can consist of dust, soot, pollen or bacteria. Pure water doesn't have to crystallize into ice until it is below zero, but in the demo here, the water has been cooled to -6 Celsius. It only freezes after the P. syringae is added.
P. syringae gets this skill from the proteins that cover its surface membrane. The proteins basically form a physical structure that water molecules latch onto. That structure also orients the molecules in a way that prompts the formation of ice crystals. It's these proteins that really serve as the instigator of ice nucleation and they're incredibly efficient at it — far more so than dust...
Commercial snow machines use the proteins (though not the bacteria itself) to help instigate the creation of snow on ski mountains.
Check it out below: [Mark Martin via Boing Boing]