Preheat oven to 325°F (165°C).
In a large bowl, combine flour, sugar, baking powder, and salt.
Make a well in the center and add egg yolks, water, oil, and vanilla. Beat until smooth.
In another bowl, beat egg whites and cream of tartar until stiff peaks form.
Gently fold egg whites into the batter until just blended.
Pour batter into an ungreased 10-inch tube pan.
Bake for 55-60 minutes or until cake springs back when lightly touched.
Invert pan immediately and let cool completely before removing cake from pan.