Last night I filled a 20 fl oz bottle (http://www.thenibble.com/reviews/main/beverages/soft-drinks/boylans-mash.asp) with lukewarm water from my tap. I filled the bottle pretty much to the brim, capped it, and put it in my freezer.
Today, I took the bottle out, and left it on the table in my far-too-hot room for 10 minutes or so. When I unscrewed the cap, water flew everywhere, like a can of soda that's been shaken up really intensely. What happened? Can anyone explain this?
Water is an unusual substance in that it expands when it freezes. Evidently this expansion wasn't enough to burst the bottle in your case, but it left the bottle's contents under pressure. After you'd defrosted it for a while there was, presumably, some ice and some water in the bottle. Because the ice was taking up more volume than it did when it was water, the liquid water in the bottle was pressurised. I expect that the bottle's sides were bowed out slightly to accommodate the extra volume. When you unscrewed the cap, the pressure forced the liquid water out of the bottle. Essentially (I would guess) it was being pushed out by the slightly elastic sides of the bottle contracting back to their usual shape.
