Water is the most abundant molecule in a cell. Approximately 70 percent of a cell's mass is composed of water molecules. The composition of the rest of the cell is organic molecules and inorganic ions.
Although important to the cell, the inorganic ions make up only about 1 percent of the cell's mass. The remainder of the cell's mass is composed of organic molecules. These are usually carbohydrates, nucleic acids, lipids or proteins. Since the oxygen in water has a slightly negative charge and the hydrogen a slightly positive charge, water is polar and is able to react with ions as well as form hydrogen bonds.