How does water increase in volume when frozen?

Most liquids have a quite simple behavior when they are cooled (at a fixed pressure): they shrink. The liquid contracts as it is cooled; because the molecules are moving slower they are less able to overcome the attractive intermolecular forces drawing them closer to each other. read more

The answer to your question is that, in general, a given volume of liquid water at room temperature will increase in volume by about 9.05% after freezing. Most materials do the opposite, that is, the solid form of most substances is more dense than their liquid form. read more