Arrange rolls in a 9×13-inch baking dish, cover the dish with plastic wrap, and let rise until doubled in size, about 30 minutes.
Combine 14 ounces water, coconut milk, and sugar in a saucepan. Whisk remaining water and cornstarch together in a small bowl. Bring coconut milk mixture to a boil, whisk in cornstarch mixture, reduce heat to medium-low, and simmer, stirring occasionally, until sauce thickens, about 3 minutes.
Preheat oven to 350 degrees F (175 degrees C). Remove plastic wrap from rolls.
Bake rolls in the preheated oven for 10 minutes. Pour coconut sauce over rolls until at least half of each roll is covered in sauce. Return rolls to oven; continue baking until rolls are golden brown, 5 to 10 minutes more. Cool in the baking dish, 3 to 5 minutes, before serving warm.