Preheat your oven to 325°F (165°C).
In a large mixing bowl, combine the cake flour, 1 cup of sugar, baking powder, and salt.
Make a well in the center of the flour mixture. Add the egg yolks, water, oil, and vanilla extract. Beat until smooth.
In another bowl, beat the egg whites and cream of tartar until soft peaks form. Gradually add the remaining ½ cup of sugar, beating until stiff peaks form.
Gently fold the egg whites into the batter until just blended. Do not overmix.
Pour the batter into an ungreased 10-inch tube pan. Bake for 55-60 minutes or until the cake springs back when lightly touched.
Invert the pan immediately and let it cool completely before removing the cake.