Water is a polar molecule.It is a covalent molecule with no overall charge but there is a slightly uneven distribution of electrons between the oxygen atom and the hydrogen atoms. This makes the hydrogen atoms slightly positive and the oxygen atom slightly negative.Unlike charges attract so the oxygen atom of one water molecule and the hydrogen atom of another water molecule will attract each other. The bond formed by this attraction is called a hydrogen bond.The hydrogen bonding in water molecules is responsible for its unusual properties such as a high specific heat capacity and a high latent heat of vaporisation, cohesion of the water molecules, a high surface tension and the anomalous expansion of water with temperature.