The name given to the bond between water molecules is a hydrogen bond. These bonds occur between the slightly negative oxygen of one water molecule and the slightly positive hydrogen of another water molecule. Hydrogen bonding gives water special physical properties.
The differences in electronegativity between hydrogen and oxygen lead to an unequal sharing of electrons. Electronegativity measures how strongly an atom attracts electrons. Oxygen, with its higher electronegativity, pulls on the shared electrons more, giving the oxygen atom a partial net negative charge. The shared electrons spend less time with the hydrogen atoms; therefore, the hydrogen regions of water have partial positive charges.