What makes water, H2O, a polar molecule?

Its density, as liquid water, is more than that of ice.
It has hydrogen bonds.
Its hydrogen atoms have a greater electron affinity than its oxygen atom.

Its structure is asymmetrical causing a positive and negative pole.

The unequal sharing of electrons between the oxygen and hydrogen atoms in water creates a polar covalent bond. This causes the oxygen atom to have a slight negative charge, while the hydrogen atoms have a slight positive charge. Due to this unequal distribution of charge, water molecules exhibit a positive and negative pole, making it a polar molecule.