Liquids generally have a lower density as compared to solids. But the solid form of water, i.e., ice floats on the surface of liquid water. It indicates that the density of the solid form of water is lower than the liquid form of water. This is due to the open cage-like structure of ice. It means, in ice, some vacant spaces are left when H2O molecules get linked in ice. In water, these vacant spaces are less. Therefore, due to the larger vacant spaces, the volume of ice increases hence, density decreases. Thus, it floats over the surface of the water.