Preheat the oven to 325°. In a large bowl, combine the flour, sugar, baking powder and salt. Make a well in the center; add the water, egg yolks, oil, lemon zest and vanilla. Whisk the dry ingredients into the yolk mixture until the batter is blended and smooth. Set aside.
In a large mixer bowl, beat the egg whites and the cream of tartar at medium-low speed until foamy. Gradually increase the speed to high and beat the whites until stiff (but not dry) peaks form. Gently fold 1/3 of the beaten whites into the batter with a rubber spatula just until blended. Fold in the remaining whites just until combined. Pour the batter into an ungreased 10-inch tube pan.
Bake 1 hour, or until the top springs back when lightly touched with a fingertip and a cake tester inserted into the center comes out clean. Invert the pan onto the neck of a wine bottle or a large funnel. Cool completely.
In a medium bowl, whisk together the glaze ingredients until smooth.
Remove the cake pan from the bottle. Run a long thin knife around both edges of the cake pan. Invert the cake onto a serving plate and remove the pan. Spread the icing on top of the cake, allowing some of the glaze to drip down the sides.