In freezing water into ice cubes, the mass remains the same but the volume increases. The increase in volume confers a reduction in density between ice and water.
Like most chemical reactions, in phase changes, mass is always conserved. This applies to the freezing of water. When water is frozen, it mass stays the same. Freezing water in turn causes a spike in volume which leads a decrease in density. This is why ice floats on ocean water, an anomalous behavior.
