In many preparations, particularly ones based on surfactants, water is the major ingredient and, as such, justifies first place in the list of chemicals. When studying formulations that are water based there is often a temptation to view the water's role as simply one of diluting the preparation to make it go further. But this versatile liquid is not to be thought of lightly. Water plays a vital role in most everyday formulations and so an understanding of it is essential; and without this it is impossible to get a grasp of the way in which many other chemicals work.

In attempting to understand how water behaves we must, just as with other chemicals, consider the structure of its molecules. Two hydrogen atoms covalently bonded to a single oxygen atom give the water molecule its unique and fascinating properties, both physical and chemical. The hydrogen oxygen covalent bond is highly polar because of the large difference in electronegativity of these two atoms.

Most of us have seen how a jet of water from a burette is bent by the electrostatic attraction of charged plastic rod placed near the jet. The polar bonds make water a polar liquid and this has important consequences as will be discussed in the section on solvents and dissolving.

At any one time a small number of these highly polar molecules will undergo complete polarization, resulting in a covalent bond breaking and dissociation into two ions. This gives rise to an equilibrium from which is...