The covalent bonds between hydrogen and oxygen in a molecule of water are the most polar. Water is a covalent molecule, meaning the two atoms of hydrogen and the one atom of oxygen share electrons.
In an ionic molecule, the electrons are donated by one atom and grabbed by another, as in a molecule of table salt. This gives the molecule a positive or negative charge, making it an ion. Ions have positive and negative poles much like a magnet. In the case of water, the electrons tend to stay in the vicinity of the oxygen molecule, even though there is no ionic bond. This makes the molecule polar.