In a small pot over medium heat, combine 1/2 cup coconut water with the sugar. Heat until the sugar has dissolved. Remove from the heat, add the lime juice and let cool to room temperature, about 20 minutes.
Place the coconut shavings on a small plate. Dip the rims of 4 margarita glasses into the coconut simple syrup just to dampen. Invert the glasses onto the coconut to coat the rims. Fill the glasses with ice.