Club soda and tonic water are two popular forms of carbonated soda water. Both have substances added to impart flavor to the pure carbonated water, and both are used for mixing drinks. The big difference between them is that tonic water contains quinine and sugar that give this beverage its distinctive sweetly bitter flavor, according to the Boston Globe. That means tonic water has calories while club soda does not.
Tonic water was developed in the 19th century by British colonists in tropical countries as a medicine against malaria, according to the Boston Globe. Quinine was the active ingredient. The colonists added gin and sugar to counter the bitter quinine taste, creating the drink known as gin and tonic. Tonic water sold today contains only 83 mg of quinine per liter, less than half a percent of the therapeutic dose. Club soda, by contrast, is simply carbonated water with minerals added to emulate the flavor of naturally carbonated mineral waters.
Tonic water, according to Schweppes, contains carbonated water, high-fructose corn syrup and/or sugar, citric acid, natural flavorings (fruit extracts) and quinine, plus sodium benzoate as a preservative. Their club soda contains carbonated water, potassium sulfate, sodium bicarbonate (baking soda) and sodium chloride (salt). Other bottlers use different blends of minerals in their club sodas.
Tonic water typically has 83 calories per 8-oz. cup with 21.5 gm of sugar (7 percent of recommended daily allowance), 29 mg of sodium (1 percent of RDA) and 2.4 mg of calcium. A typical club soda, by contrast, has zero calories, 50 mg of sodium (2 percent of RDA), 11.8 mg of calcium and 4.7 mg of potassium.