At least according to [link|http://www.gi.alaska.edu/ScienceForum/ASF4/440.html|this] discussion of water freezing in pipes. In an open container, [link|http://www.gi.alaska.edu/ScienceForum/ASF6/650.html|this] discussion of water freezing in a cup, they say that it depends on the environment the water is in:

I never put much credence into these claims until I started reading different accounts of the phenomenon. Most recently, the distinguished scientist and author, Isaac Asimov, in his Book of Facts (Red Dembner Enterprises Corp., 1981), flatly states in one of his "3000 facts," that "Water freezes faster if it is cooled rapidly from a relatively warm temperature than if it is cooled at the same rate from a lower temperature."

This may be true, but only under certain circumstance. Dr. T. Neil Davis (editor of this column from 1976 to 1981) performed his own experiments, and found that only when he used Styrofoam cups at temperatures near zero, did warm water freeze first.

Under almost any other circumstance, especially those which allowed heat to escape through the sides of the container, such as from a metal cup, the colder water froze first.

Insulation being taken into account, we can now attribute the hot water freezing first to the fact that, in hot water, circulation currents move faster, exposing more water to the air, and resultant evaporation (hence, cooling) occurs at a greater rate. Also, boiling the water before exposure to frigid temperatures removes the dissolved air which inhibits freezing in the colder water.


Nothing's simple... :-)

Cheers,
Scott.