Add rum, coconut water, lime juice, and simple syrup.
Shake about 10 seconds until well-chilled.
Fill a chilled highball glass with fresh ice and strain the cocktail into the glass.
Garnish with a lime wedge.
Notes
Coconut water provides gentle sweetness and a smooth finish—keep it cold for the best texture. Adjust sweetness with more or less simple syrup, and brighten with an extra squeeze of lime if desired.Pairs nicely with grilled seafood and light snacks. For variation, try a dash of bitters or a flavored rum.