In large bowl, stir together flour, granulated sugar, baking powder, and salt. In another large bowl, combine water, cooking oil, egg yolks, orange peel, and vanilla.
Make well in center of flour mixture; add egg yolk mixture. Beat with electric mixer on low speed until combined.
Wash beaters thoroughly. In a large bowl, beat egg whites on high speed until frothy. Beat in cream of tartar and continue beating just until stiff peaks form (tips stand straight). Pour egg-yolk batter in a thin steam over entire surface of beaten egg whites; fold in lightly by hand. Pour batter into an ungreased 10-inch tube pan.
Bake in a 325 degree F oven for 55 to 60 minutes or until top of cake springs back when touched lightly. Remove from oven; invert in its pan. Cool in pan.
Gently loosen side of cake from pan with a spatula or knife. Invert onto a serving plate and remove pan. Sift powdered sugar over cake. Makes 12 servings.