Preheat oven to 350^F. Beat egg yolks and sugar until light and fluffy (about 7 minutes). Add cold water, orange juice, orange rind, chocolate and cake flour. Gently fold in stiffly beaten egg whites. Pour into a 25 cm tube pan with removable insert. Bake for 55 to 65 minutes or until cake springs back when gently pressed. Cool completely, inverted on cake rack, before removing from pan.