Does water expand when it freezes?

When water freezes, it becomes crystalline and the crystal matrix takes up more space than the unaligned free water molecules. There's a good illustrated explanation here: http://www.iapws.org/faq1/freeze.htm Actually, water is at its densest at 4°C. As it cools beyond that, it expands until it freezes.

Yes the molecules of water packs tighter, but as they bond together they form hexagons, which creates more space in between them than before. That is how the ice expands.