Pour the rum, coconut water, liqueur, pineapple juice, lime juice, and syrup into a heatsafe mixing bowl.
Over medium-low heat, heat the milk in a saucepan, stirring continuously until the milk begins to bubble around the edges (taking care not to let it boil).
Add the milk to the mixing bowl, stir until it begins to coagulate, and let the mixture sit for 15 minutes.
Strain twice. First through a cheesecloth, and second, through a coffee filter until the mixture is clarified.
Ladle into cups over ice, and garnish with a citrus peel, cherry, or pineapple slice.