Why water's O to H bonds are so highly polar?

This is due to the difference in electronegativity of H
and O.

Electronegativity is the relative tendency of an
atom in a bonding to attract the bonded electron pair towards itself. Greater the value
of electronegativity, greater the tendency. In Pauling Scale of electronegativity the
maximum value is for Fluorine = 4.

In water the
electronegativity value for O = 3.5 and for H = 2.1

Due to
this difference, oxygen will attract, the  H--O--H electon pair between  oxygen and two
hydrogen atoms, towards oxygen and become doubly negatively charged. So the two H aoms
are positive charged.

This charge seperation, resulting
from the difference in electronegativity, is the reson for the polar nature of
water.

We can see that H-H (hydrogen molecule) or O=O
(oxygen molecules are non-polar because the difference in electronegativity of H-H, or
O=O, in these type of  molecules  are zero.