@Afos22 and @Lightlyseared, Yes, the CO2 does take up space, and does not simply “sit between molecules”, at least not without some effect. However, the actual space taken up is incredibly minuscule. Seriously, we’re on the scale of displacing maybe a few dozen molecules. Perhaps up to a hundred or two. You’d have to have, maybe, the entire Atlantic ocean’s worth of carbonated water to really notice the difference without some expensive and complex machinery.
@Lightlyseared and @BoBo1946 The carbon dioxide does acidify the water, but again, it’s a small amount. I’d be surprised if it caused much of an effect without long-term, high-level exposure. Like, drinking a few bottles every day for several years. If you have evidence to the contrary please let me know, but intuitively that doesn’t quite make sense. Also keep in mind soda =/ sparkling water. Soda has a ton of other stuff which could very well acidify the drink to noticeable levels.
In general, I’d agree with @marinelife. The biggest effect is sure to be the carbonation in your stomach, you simply can’t down enough after a lot of exercise without running out of room in your stomach. So after exercise, it’s bad, but in general it’s probably fine.