Melt butter in a 13x9x2-inch baking pan. Add water; sprinkle with the sugar, nuts, then coconut. Set aside.
Prepare cake mix according to package directions. Pour batter evenly over nut and coconut mixture in the baking pan.
Bake at 350° for 35 to 40 minutes, or until cake springs back when lightly touched with finger. Let cake cool in pan for 5 minutes; turn upside down onto platter or cake plate or other large flat dish. Serve with whipped cream or whipped topping, if desired.