It's a long answer but here it is. There are 2 main components that make water polar: the shape of the molecule and the electronegativity of the atoms.
Water is H2O, hydrogen is less electronegative compared to oxygen meaning that oxygen has more energy to pull electrons to them thus allowing hydrogen to bond with it. So when hydrogen bonds with oxygen, the oxygen pulls hydrogen's electron closer to oxygen than to hydrogen in the covalent bond, this causes hydrogen to be slightly positive and oxygen to be slightly negative.
The shape of the molecules should be considered as well, water is non linear molecule and is bent because of the lone pair electrons repel the paired electrons, this makes
one part of the molecule to be more positive and the other to be more negative.