Beat egg yolks with water, lemon juice and sugar until light and fluffy (3 minutes at medium speed using an electric mixer).
Gradually add cake meal, potato starch and lemon rind and continue beating for an additional 2 minutes at medium speed.
Beat egg whites with salt until a very firm peak is formed, and fold beaten egg whites into batter gently but thoroughly.
Pour into an ungreased 10 inch tube pan, and bake in oven at 350º F for 1 hour and 10 minutes, or until cake springs back when touched lightly with a finger.
Invert pan and cool thoroughly before removing from pan.