There are other gasses that can be added to flavoured water to make it fizzy and not toxic, you can add oxygen or nitrogen but they have their own issues, oxygen fizzy water tastes flat and makes the water taste oxidized.
~image generated by artificial intelligence (chatGPT)
Nitrogen gas costs more than carbon dioxide and it is more difficult to dissolve in water so it makes the water less fizzy and the bubbles are smaller so the foam caused by pouring the liquid lasts a long time. Some beer companies have been known to use Nitrogen instead of Carbon dioxide because they don't want a tangy taste and they want the pouring foam to last a long time.
Most carbon dioxide gas in fizzy drinks is a by-product of other industrial process so it is very cheap. They almost treat it like a waste product, yet for a fizzy drink it is the best gas to use, you get more fizz, a tangy taste from the drink and you get a longer shelf life because carbon dioxide is acidic when dissolved in water and that kills microbes.
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