Cocktails with Tonic water
Tonic water is a carbonated soft drink flavored with quinine, which gives it a distinctive dry bitterness.
Substitutes for Tonic water
Quinine is the whole point, and plain carbonated water does not have it — a tonic-less highball is a different drink, not a weaker one. If you build it from parts, the sweetness is yours to set, which is more control than any bottle gives.
Often confused with
Plain carbonated water, sometimes with a pinch of mineral salts; no quinine and no sugar, so a highball built on tonic comes out sour and thin with it.
Also quinine-based, but with lemon juice and peel flavor added over the bitterness. It brings its own sweetness and acidity, so cut the citrus back or the drink comes out sweet and blurred.
Storage
Loses its fizz fast once opened. Keep it sealed and chilled, and pour a fresh bottle for each round instead of reusing a half-flat one.
