about intermolecular force

Van der Waals forces(London dispersion forces) involve the attraction between TEMPORARILY induced dipoles in nonpolar molecules (often disappear within an instant).

Diploe-diploe attractions are the forces that occur between two molecules with PERMANENT dipoles.

Between water molecules, there is Diploe-Dipole attraction because H2O is a Permanent Dipole.

Between H and O, there is Van der Waals force.

Hydrogen atom and oxygen atom are held by covalent bond but H2O molecule are held by week van der waals' forces.