In medium bowl mix flour and salt. With pastry blender or 2 knives, cut in margarine until mixture resembles fine crumbs. Sprinkle water over flour mixture while tossing with fork to blend well. Press dough firmly into ball. On lightly floured surface roll out to 12-inch circle. Fit loosely into 9-inch pie plate. Trim and flute edge. Fill and bake according to recipe.