Add the mint leaves, sugar or simple syrup, and lime juice to a tall highball glass.
Press the mint gently a few times with a muddler or the back of a spoon to release the oils. Don't over-muddle.
Fill the glass with ice.
Pour over the coconut water and soda water.
Stir gently and garnish with a fresh mint sprig and a lime wedge.
Notes
Press the mint gently, just enough to release the oils. Over-muddling shreds the leaves and makes the drink bitter.If using simple syrup instead of sugar, add it with the lime juice before pressing the mint.Swap the coconut water for more soda water if you prefer a classic base.To make for a crowd, multiply and build in a pitcher. Add the soda water just before serving.