Water is composed of two atoms of Hydrogen and one atom of oxygen. When covalently bound together, this molecule is polar. Because a covalent bond is a sharing of electrons between two or more atoms. In the case of water, oxygen shares an electron with each of two hydrogen atoms. At any one point in time, the oxygen side of the water molecule is slightly negative while each of the two hydrogen molecules are slightly positive. This is the effect of adding or subtracting a negatively charged electron. This type of bond is called a hydrogen bond and is a very low energy bond.