Water is the most essential compound in the world. The earth contains a total of 75% water, whereas the other 25% is land, desert or anything other than water. Water is mostly responsible for all life forms that are found on planet Earth. Humans, animals, plants, and all other forms of life depend on the consumption of water for their survival, thus making this compound an essentially vital factor contributing towards the survival of all species living in the world.
Water is a compound that contains one atom of oxygen and two atoms of hydrogen. The two atoms of the hydrogen element are covalently bonded to one of the atoms of oxygen, thus forming H2O. This covalent bond is made possible due to the sharing of two hydrogen electrons with that of the oxygen atom.
The concept of polarity arises due to the formation of the covalent bond between hydrogen and oxygen. Generally, one of the properties of a covalent bond is that the electrons that allow the formation of the bond to occur will be equally shared between both elements sharing them. That is, when a covalent bond occurs between hydrogen and oxygen, the electrons should be shared equally between both hydrogen and oxygen.
However, such is not the case with water. The oxygen in the water compound attracts the electrons with a stronger force when compared to hydrogen. Thus, the level of attraction generated by oxygen atoms force an uneven charge distribution. This irregular or asymmetrical distribution of charge is what causes polarity to occur, where atoms have somewhat of a negative charge and also a positive charge as well.
Polarity allows outside or external molecules (learn details about difference between molecules and compounds) to mix in quite easily with water. The property of polarity is important mainly because it serves as an essential characteristic aiding in the survival of living organisms. In general terms, the bonds formed by hydrogen are not as strong as the bonds formed by normal covalent bonds, but in the case of water, the bond is strong enough.
Polarity helps water to be transported from lower levels to higher levels in trees and plants through their vessels, thus making it an essential characteristic deemed vital for the survival of plants. Polarity also can be related to the importance of adhesion of water. The force of adhesion is what allows the water molecules to bond with other substances; again without polarity, this force would not be possible to generate.
Source: http://www.buzzle.com/articles/why-is-water-a-polar-molecule.html
