Heat oven to 350 degree. Grease bottom only of a 13X9 pan with shortening or spray bottom with cooking spray.
In a large bowl, beat the cake mix, water, oil, and eggs with electric mixer on low speed for 30 seconds. Beat on medium speed for 2 minutes, scrap bowl occasionally. Pour into pan.
Bake 33-38 minutes or until toothpick comes out clean. Cool 15 minutes.
In a small bowl, mix lemonade concentrate and powder sugar. Pierce top of warm cake every 1/2 inch. Drizzle lemonade mixture evenly over top of cake. Run knife around side of pan to loosen cake. Cover and refrigerate 2 hours.
Spread frosting over top of cake. Store in refrigerator.