Line bottom of a 9 in. (23 cm) cake pan with waxed paper, (Do not grease bottom or sides of pan.
Do not use a smaller cake pan; this cake will fill a 9 in. (23 cm) pan.) Combine cake mix and water in a mixing bowl.
Beat on low just until mixed.
Then beat on high for 2 minutes.
Add egg whites, and beat on high for 5 to 7 minutes.
Transfer cake batter to pan.
Bake at 350°F (175°C) for 35 to 40 minutes or until pick inserted in middle comes out clean.
Do not underbake.
Allow cake to cool in pan for 10 minutes.
Carefully slip a knife around the outside edge of the cake, invert to a cooling rack, and remove waxed paper.
Invert to right-side-up position.
Cool completely.