Pour the gelatin mix into a (2-3 cup) liquid measuring cup. Heat the water in a small saucepan until it comes to a boil (or you can put it in a microwave-safe bowl or measuring cup and heat it in the microwave).
Pour the boiling water over the gelatin and stir until the gelatin is completely dissolved. Add the coconut rum; stir to blend.
Fill each portion cup and place in the refrigerator until set.