Dangerous..Worth a read

[Mike Abberton]

I believe that purity of the water has something to do with it. The less particles in the water, the less bubble-forming sites (or crystal forming sites for super-cooled water). The prevalence of today's filtered water probably only makes this phenomenom more likely to happen.

Another example of this is the "mentos in diet coke" fountain effect. Mythbusters did a show where they tested the fountain effect and it appeared that the crucial element to the fountain were the large number of small pits and crevices on the mentos candy shell.