Prepare pie crust. Wash and drain blueberries. Remove stems if necessary. Reserve 2 cups berries for sauce and fill prebaked pie shell with remaining berries. Combine sugar and cornstarch in a saucepan. Add water and bring to a simmer. Cook until liquid thickens, about 3 minutes. Add reserved berries and simmer 5 minutes, stirring constantly, or until sauce is thick and clear, not cloudy. Spoon over blueberries in pie shell. Place in refrigerator to set.