Preheat oven to 350 F
Spray an 8x8 square dish with nonstick cooking spray
Combine cake mix, eggs and vegetable oil until just combined and all lumps are smooth - do not not over mix! Batter will be very thick.
Pour into greased baking dish and bake 30-32 minutes, or until brownies are set (brownies will continue to cook and firm up a little while cooling, but you want them to still be a little dense in the middle)
In a separate bowl, whisk together powdered sugar and water and pour over brownies while they're still warm.
Allow brownies to mostly cool before cutting