In large mixer bowl blend 1 cup shortening, 1 1/2 teaspoons cream of tartar, 1 1/2 teaspoon vanilla and dash of salt. Beat in 3 pounds sifted powdered sugar alternately with 3/4 cup water. Beat until frosting is smooth. Blend in additional water, 1 teaspoon at a time, if necessary to thin the frosting to spreading consistency.