If you really want to get fancy, you can even make or buy your own tonic syrup, allowing you to play with just how much tonic flavor is each drink. There are lots of recipes floating around online, but if you just want to let someone else do the work, the Darlingtons recommends Jack Rudy tonic syrup , which typically retails anywhere from $15-20 but can sit in the fridge and be added to seltzer water whenever you want, reducing the chances that extra tonic water will go to waste. Especially if you have your own SodaStream, you can make exactly the amount of tonic water you need with no waste.