Separate the eggs, putting the egg yolks in one bowl and egg whites in another. Set aside.
In a large bowl, sift together the flour, sugar, baking powder and salt. Set aside.
In another bowl, mix together the egg YOLKS, water, oil, orange zest and vanilla.
Pour the wet ingredients into the dry and mix until well combined.
Add the cream of tartar to the egg whites. Using a stand mixer, beat until the peaks are stiff. (This took about 4 minutes in a stand mixer.)
Gently fold the egg white mixture into the batter until combined. Batter will be very light and fluffy.
Pour into an ungreased tube pan (with a removable bottom) and bake on the lowest rack for 50 minutes, or until top springs back when touched.
Immediately invert the pan and let it rest upside down on three glasses.
Allow the cake to cool upside down completely, then slide a knife around the sides and center of the pan to loosen the cake.
Remove the cake to a plate.
To make the orange glaze, whisk together the sugar, orange zest and orange juice. Add ½ to 1 tablespoon of heavy cream if the glaze is still too thick.
Drizzle the cake with the orange glaze.
Store in an airtight container at room temperature.
The calories shown are based on the cake being cut into 12 pieces, with 1 serving being 1 slice of cake. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate. **We are not dietitians and recommend you seek a nutritionist for exact nutritional information. The information in the nutrition box are calculated through a program and there is room for error. If you need an accurate count, I recommend running the ingredients through your favorite nutrition calculator.**