What would be heavier to lift? A bucket of water or a bucket of ice?
The bucket of water, of course!
Try this experiment.
Half fill an empty vessel with water and carefully measure the space between the surface of the water and the top of the vessel.
Place the vessel in the freezer. When the water has frozen into a solid, measure the space between the top of the ice and the top of the vessel. You will find that the space is much less now. Leave the ice to thaw out and you will find that the water occupies the same volume as it did before you froze it.
If you add more water to bring the level of water to the level the ice had reached, the vessel will definitely become heavier.
What does this suggest? That ice is lighter or less dense than water.