In a clean bowl, beat egg whites on medium speed until foamy.
Add cream of tartar and continue beating.
Gradually add 1/2 cup sugar, one tablespoon at a time, beating until stiff, glossy peaks form (2-3 minutes).
In separate bowl, whisk egg yolks with remaining 1/2 cup sugar, water, and vanilla until pale yellow and thick (about 2 minutes).
Sift one-third of flour over egg whites and gently fold using circular motion from bottom up.
Repeat folding with remaining flour in two more additions.
Fold yolk mixture into batter in three additions, being careful not to deflate egg whites.
Pour batter into ungreased tube pan and gently smooth the top.