Mix the cake mix with the water, oil and eggs according to package instructions and pour into a 9x13" pan. Bake for 28 to 33 minutes. Let cool for 15 minutes.
Poke a fork, many times, into the top of the warm cake. Meanwhile whisk together the 1 cup lemonade concentrate with 1 cup powdered sugar. Pour evenly over the cake. Let soak in until the cake has cooled to room temperature. Cover and refrigerate until chilled, about 1 hour.
For the Frosting:
Beat the cream cheese and butter until light and fluffy. Gradually add the powdered sugar and lemonade concentrate (with one pinch of salt) and mix until light and fluffy.
Spread the frosting over the cake. Slice and enjoy!