Add cake mix, smartwater® sparkling water, vegetable oil and eggs to large bowl.
Beat on medium speed until thoroughly combined.
Pour batter into a microwave safe baking pan. (see note)
Place half of the frosting into a piping bag and spread in an even layer around the top of the cake.
Microwave on high for 9 minutes.
Remove from microwave and immediately remove the cake from the pan.
Microwave the remaining frosting on high for 30 second increments, until melted.
Drizzle melted frosting on top of the cake.