Seltzer water is actually quite simple! It doesn't have any active ingredients, as it's essentially just carbonated water. Here's a breakdown:

* Water: This is the main ingredient, usually purified.

* Carbon dioxide (CO2): This is what creates the bubbles and gives seltzer its characteristic fizz.

Some brands might add a tiny bit of mineral salts for taste or to mimic the properties of naturally carbonated mineral water. However, the vast majority of seltzer water is just plain carbonated water.