Heat oven to 325°F. Grease pans; line bottoms with waxed paper; grease paper; dust pans with flour.
Mix flour, baking powder and salt on waxed paper.
With mixer on medium, beat butter and sugar in bowl until light and fluffy. Add whites, one at a time, beating after each. Beat in vanilla.
On low, beat flour mixture alternately with water into butter mixture, beating after each addition. Pour batter into prepared pans.
35 minutes, for 9-inch rounds; 30 minutes for 9-inch squares; 45 minutes for hearts; 55 minutes for 10-inch round, or until wooden pick inserted in center comes out clean.
Cool pans on rack 10 minutes. Remove cakes to cool.