Preheat Oven to 350 Degrees. Grease a 9 x 13 inch baking dish. Spread the raw rhubarb evenly in the bottom of the baking dish. Sprinkle the sugar evenly over the rhubarb followed by the Jello and then the cake mix. Pour the water and melted butter over the top. DO NOT STIR. Bake at 350 Degrees for 45 minutes or until the rhubarb is tender.