1. Prepare blueberries: Rinse and sort blueberries. Put them in a sauce pan with the water and cornstarch. Cook and lightly stir until thickened on medium to low heat. Cool and put in refrigerator to chill.
2. Mix crust: mix margarine, powdered sugar and flour. Cut the above together and refrigerate for 1/2 hour. Then press the crust into a 9 by 13 inch pan and bake 10 minutes at 350°F.
3. Prepare filling: Mix sugar and cream cheese, add Cool Whip. Put into crust and chill 1/2 hour. Add chilled blueberry mixture and chill for 1 hour. Then enjoy.