Why density of water is greater than ice ?

Ice and water both contains H2O molecules but in water H2O molecules are more compactly arrange than in ice.

Ice has a hexagonal cage like structure, inside it H2O molecules are not closely packed.hence there is more vacant space between the molecules of ice. As a result the volume increases due to the vacant spaces.  As a result density of ice decrease.

Other hand,On increasing temperature then kinetic energy of molecules increases as result the interaction between the molecules decrease and as a result the the molecules come closer to each other and the volume decreases, so the density increases.

The density of water is maximum at 3.98 ℃ approximately 4 degree celsius.