Bake the Cake
Preheat the oven to 350°F (175°C). Grease and flour a 9x13-inch baking pan or line it with parchment paper.
Prepare the white cake mix according to the package instructions and pour it into the prepared pan.
Bake for the time specified on the box (usually 28-32 minutes) or until a toothpick inserted into the center comes out clean. Remove from the oven and let cool slightly.
Prepare the Cranberry Mixture
In a small saucepan, combine the cranberry sauce and water. Heat over medium heat, whisking until smooth and slightly thinned. Remove from heat and let cool slightly.
Poke the Cake
Once the cake has cooled for about 15 minutes, use a wooden skewer or fork to poke holes evenly across the surface of the cake.
Pour the cranberry mixture over the cake, ensuring it seeps into the holes. Spread any excess sauce evenly over the top with a spatula.
Add the Whipped Topping
Allow the cake to cool completely, then spread the whipped topping over the cranberry layer. Smooth it with an offset spatula for an even finish.
Garnish and Serve