Which tonic for this gin? Probably one of the most asked questions when it comes to exploring the world of tonics and gins. But what is tonic water? What is Indian tonic? Why is tonic water so bitter and where does quinine come from? Fruitful, sweet, dry or black tonic water: Learn all about this mixer and what else you could use when there is no tonic around, like syrups, cordials, tea or other soft drinks.