In a mixing bowl combine cake mix, pudding mix, and eggs. Mix well with mixer. Add milk and melted margarine, cream cheese and water and continue mixing. Batter will be thick. Fold in blueberries and walnut pieces. Spray your cake pan well. Cook in preheated 350 degrees oven for 55 to 60 minutes until center is cooked. Let stand for 15 to 20 minutes before removing from pan.