HEAT oven to 350°F.
PREPARE cake batter as directed on package; pour into 13x9-inch baking dish sprayed with cooking spray.
BEAT dry pudding mixes, sugar, milk and water with whisk 2 min.; pour over batter. Place baking dish on baking sheet.
BAKE 55 min. to 1 hour or until toothpick inserted in centre of cake layer comes out clean. Cool 20 min. (Sauce will thicken slightly as it cools.) Spoon into serving dishes; top with Cool Whip.