What exactly is it that makes club soda different from tonic water? The answer is super simple, but it makes a ton of difference in regards to taste. Club soda is made by adding mineral salts and carbon dioxide to water. Seltzer water is made with carbonation but without the added minerals (via Healthline). Club soda tends to be plain or come in a small variety of simple flavors, and its best utilized when you're looking to add bubbles to a cocktail. Add a bit on top to kick up a simple drink (via Advanced Mixology).
Tonic water is also made by adding carbon dioxide to water, but that's where its similarities with club soda end. Thanks to the added sugar, it adds a bitter and slightly sweet flavor to your cocktail. It also contains quinine and tops cocktails with a nice bit of bubbles for a perfect finish. According to Advanced Mixology, tonic water tends to be superior when it comes to tending bar.
