Place watermelon in a blender or small food processor. Cover and process until liquefied. Fill a cocktail shaker with ice then add pureed watermelon, coconut water and vodka to the shaker; squeeze juice from half of the lime into the shaker. Vigorously shake the cocktail. Strain into two chilled martini glasses.

Cut the other half of the lime into two wedges. Skewer a lime wedge and a watermelon wedge on each of two cocktail picks; garnish each glass with one of the skewers.