Tonic water (or
Indian tonic water) is a
carbonated soft drink flavored with
quinine.
The drink gains its name from the medicinal effects of this slightly
bitter flavoring. The quinine was added to the drink as a
prophylactic against
malaria, since it was originally intended for consumption in tropical areas of
India and
Africa where that disease is
endemic.
Tonic water originally contained only
carbonated water and a large amount of quinine. However, most tonic water today contains a medically insignificant amount of quinine, and is thus used for its flavor only. It is consequently less bitter, and is also usually sweetened. Some manufacturers also produce diet tonic water. In the
United States, the
Food and Drug Administration limits the quinine content in tonic water to 83
ppm (83 mg per liter if calculated by mass), which is one-half to one-quarter the concentration used in therapeutic tonic.
Tonic water is often used as a
drink mixer for
cocktails, especially those made with
gin (for example, a
gin and tonic). Tonic water with
lemon or
lime flavor added is known as
bitter lemon or
bitter lime, respectively. Such
soft drinks are more popular in
Europe than in the
United States.
Tonic water will fluoresce under
ultraviolet light, due to the presence of quinine. In fact, the sensitivity of quinine to ultraviolet light (UV) is such that it will fluoresce in direct sunlight.