Back in my high school chemistry class this effect was noted and explained in the following way: Ice needs to form a particular crystalline structure when it f

Back in my high school chemistry class this effect was noted and explained in the following way: Ice needs to form a particular crystalline structure when it freezes. This is what makes ice float in water. The molecules in warm water are moving faster and therefore have a greater chance to wander into this correct formation. The cold water molecules are moving more slowly and simply take more time to find the correct alignment. There wasn't really any proof to this theory, but it was followed with a bunch of anecdotal evidence, like Canadian's washing their cars with cold water, etc.