Tonic water

Canada Dry Tonic Water

From Wikipedia:

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

From the HD Forums:

• Making Tonic Water and Safe Quinine levels