Question

WHAT IS THE FOURMULA OF CARBONATED WATER

Answer 1

When carbon dioxide is dissolve in water it form carbonic acid.
H2O + CO2 ⇒ H2CO3
this acis is the carbonated water. 

Answer 2

This process of carbon dioxide when dissolved in water is generally written as
C$O_{2}$ + $H _{2}$O =$H _{2} CO _{3}$