Heat oven to 350°. Grease bottom only of rectangular pan, 13x9x2 inches, with shortening or spray bottom with cooking spray.
Beat cake mix, water, butter and eggs in large bowl with electric mixer on low speed 30 seconds. Beat on medium speed 2 minutes. Pour into pan.
Bake 27 to 33 minutes or until toothpick inserted in center comes out clean. Cool 15 minutes. Poke top of warm cake every 1/2 inch with handle of wooden spoon, wiping handle occasionally to reduce sticking. Reserve 1/2 cup caramel topping. Drizzle remaining caramel topping evenly over top of cake; let stand about 15 minutes or until caramel topping has been absorbed into cake. Run knife around side of pan to loosen cake. Cover and refrigerate about 2 hours or until chilled.
Set aside 2 tablespoons of the reserved 1/2 cup caramel topping. Stir remaining topping into frosting; spread over top of cake. Drizzle with reserved 2 tablespoons caramel topping. Store covered in refrigerator.