In a small bowl, stir together the dry mustard and the 2 Tablespoons water - set aside. In a 1 quart saucepan mix well 2/3 cup Water, 1/3 cup Cider Vinegar, 1/4 cup Sugar, 3 Tablespoons All Purpose Flour, and 1/2 teaspoon Salt. Cook over low heat about 3 minutes or until thickened, stirring constantly. Remove from heat. Stir in Mustard mixture until smooth. Cover and refrigerate.