Water is made up of one oxygen and two hydrogen atoms. Oxygen is more electronegative than hydrogen, meaning the electrons in the hydrogen-oxygen bond are slightly more attracted to the oxygen. This makes the bond polar, with oxygen being slightly negative (δ- or "delta negative") and hydrogen slightly positive (δ+ or "delta positive"). There is a weak electrostatic interaction between these partial charges, so the slightly negative oxygen of one water molecule will be weakly attracted to a slightly positive hydrogen in another water molecule.