Put fresh and uplifting in your next non alcoholic drink with bitter orange citrus fruit that mother nature provided. Bitter orange simple syrup and soda water together provide a refreshing healthy mocktail option. When I say soda water I mean club soda (water + minerals + carbon dioxide) or seltzer (water + carbon dioxide). If you use club soda it might be slightly more salty tasting while seltzer just tastes like water. To the average palate there is little perceivable difference so I am confident to say you can use them interchangeably.
There are a number of options with soda water brands. Taste them for yourself and see what you like best. For me its Schweppes does the job at a fraction of the price of other brands.