User blog comment:WolfgangBSC/The Random Chat Room/@comment-24938973-20151202183017/@comment-13740085-20151202201525

You got that reversed, Rth. When any substance cools, the movement of its component molecules slows and they get closer together. When that movement slows to a certain point, and the molecules get close enough, that substance becomes solid. Similarly, when a substance warms, the molecules move faster and get farther apart, eventually getting to a point where the substance becomes liquid, and eventually gaseous.

TL;DR, water contracts when cooled, and expands when heated.