The library sorts bubbles by where the carbon dioxide comes from, because labels do too.
Natural
The CO₂ comes up with the water from the source. Badoit and Borjomi are naturally sparkling.
Reinforced
The source gas is captured and topped back up at bottling, so the water keeps a consistent fizz. Perrier and Gerolsteiner Sprudel are listed this way.
Added CO₂
The water is carbonated at bottling. S.Pellegrino and Topo Chico are both carbonated this way.
Many brands also bottle a still version. The library marks those as still and sparkling.