Heat oven to 350. Spray a 9 x 13" baking pan w/ cooking spray. In lg bowl, combine mayonnaise, eggs and water, mix well. Stir in brownie mix just until moistened. Coarsely chop peanu butter cups. Stir into brownie mix. Pour into pan. Bake 30-35 min, or until toothpick inserted in center comes out clean.