Water is a polar molecule.Although the hydrogen and oxygen atoms are bonded with a covalent bond, the electrons are not shared equally between the hydrogen and oxygen atoms and a partial positive charge on the hydrogen and partial negative charge on the oxygen forms.This is called a dipole.As a result, the overall molecule is polar.Water molecules are therefore strongly cohesive (stick together) as they can form hydrogen bonds between the partially positive hydrogen atoms of one molecule and a partially negative oxygen atom of another.This gives water unusual properties and is the reason water has a vital role in the external and internal environment of living organisms.