Water is a great solvent. For example, it causes ionic compounds like sodium chloride (table salt) to dissociate. One of these reasons that water does is because it is polar molecule. Why would water being a polar molecule allow it to break sodium chloride into ions of sodium and chlorine through dissociation?

A polar molecule has both a partial positive and a partial negative. Since NaCl (sodium chloride) is made out of Na + and Cl - ions, the positive and negative parts of the water will pull on these ions individually since positive attracts negative and negative attracts positive. This magnetic force causes the Na + and the Cl - ions to be pulled apart.

If you stir table salt into water, the crystal lattice of NaCl will begin to dissociate into Na + and Cl - ions. (Dissociation is just a name for the process in which a compound or molecule breaks apart to form ions.) Water molecules form hydration shells around the ions: positively charged Na + ions are surrounded by partial negative charges from the oxygen ends of the water molecules, while negatively charged Cl - ions are surrounded by partial positive charges from the hydrogen ends. As the process continues, all of the ions in the table salt crystals are surrounded by hydration shells and dispersed in solution. So since water is more positive on one end and more negative on the other end compounds like NaCl start to dissolve because one of them is attracted to the partial positive side of the water and the other is attracted to the partial negative side. Then this process continues until the water kind of coats each of the atoms.