Prepare 12 glass containers or silicone molds. Each container should be able to hold 1/3 cup of liquid.
Rinse the sweet potatoes under running water and rub the skin clean. Steam the sweet potatoes until fork-tender, about 30-40 minutes.
Boil tapioca pearls, stir and cook for 10 minutes,. Then set aside for 20 minutes. Drain the tapioca pearls into a strainer and rinse under cold water until cool, stirring occasionally. Add 5 tablespoons of sugar and mix well. Divide the tapioca pearls into the prepared 12 containers.
Blend coconut milk and milk. In a small bowl, add the cold drinking water and sprinkle the gelatin over. Mix quickly and set aside for 5 minutes.
Cut the sweet potatoes and measure out 225 grams of sweet potatoes. Add to the blender with the milk. Blend until smooth. Pour into a small pot. Add the rest of the sugar and cook over medium heat until sugar is melted. Add the gelatin and turn Off heat. Stir until the gelatin is melted.
Carefully fill each container with the sweet potato mixture while stirring quickly to loosen the tapioca pearls. Refrigerate for at least 4 hours.