Fever Tree Premium Indian Tonic Water is made using naturally sourced quinine from the bark of the fever tree in the Congo, blended with spring water, Tanzanian bitter orange, and natural cane sugar. Importantly, no preservatives or artificial ingredients are ever used in any of Fever-Tree's products. If three quarters of your Gin & Tonic is tonic, then you should be using the best tonic. This is Fever-Tree's attitude to their craft, and one shared by drinkers worldwide as it has grown to become the best-selling tonic two years running. Fever-Tree Tonic is the tonic of choice used by the International Wine & Spirit Competition is assessing the quality of gins and vodkas when mixed with tonic.