If a crust of ice with a small hole in it forms over liquid water, it can trap the liquid below, leaving it no room to expand during freezing. So, as the water begins to solidify, it is forced up through the hole and begins to freeze around the hole's edge, forming a hollow, water-filled spike. ...
Spikes typically form when the ambient air is well below 0 degrees Celsius, allowing for rapid freezing—an air temperature of about –7 degrees C (20 degrees Fahrenheit) turns out to be optimal. ... Pure water works best for spike formation, as does a container with vertical sides, such as an ice tray.
So, from this the following things can be learned:
1. We had our freezer set too cold.
2. The folks at DrinkMore should use this as an ad gimmick to prove how pure their water is.