In a small saucepan, combine sugar and lime zest. Set aside for 10 minutes. Add water. Bring to a boil over medium-high heat, stirring occasionally to melt the sugar. Pour the syrup through a sieve into a glass measuring cup. Set aside to cool. Discard the zest. Measure out ¾ cup for the limeade. Save the rest for other uses.
In a medium pitcher, combine the ingredients for limeade. Taste and adjust if needed. Pour the limeade into 2 ice cube trays. Freeze for at least 6 hours.
In a blender, add 18 limeade ice cubes and gold rum. Blend well and pour into 3 serving glasses. Keep the glasses in the freezer.
Add the frozen blueberries, 6 limeade ice cubes, and drinking water into the same blender. Blend until smooth, stirring occasionally if needed. Pour into the glasses. Garnish with lime wedges and blueberries if using. Serve immediately.