Preheat the oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking dish.

Mix flour, sugar, baking soda, vanilla extract, cocoa powder, creamy salad dressing, and water in a large bowl. Pour into the greased baking dish.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 30 minutes. Cool in the pans for 10 minutes before removing to cool completely on a wire rack.