Tonic water is a carbonated soft drink in which quinine is dissolved. Originally used as a prophylactic against malaria, nowadays tonic water usually has a significantly lower quinine content and is often sweetened. It is consumed for its distinctive bitter flavor and is frequently used in mixed drinks, particularly in gin and tonic.

A soft drink is any water-based flavored drink, usually but not necessarily carbonated, and typically including added sweetener. Flavors used can be natural or artificial. The sweetener may be a sugar, high-fructose corn syrup, fruit juice, a sugar substitute, or some combination of these. Soft drinks may also contain caffeine, colorings, preservatives and other ingredients.