Place dries (flour, baking powder, baking soda, salt) in a bowl, stir well, and set aside. In a large bowl, beat egg whites on high speed of an electric beater until stiff peaks form; set aside.
Combine water and fresh-squeezed orange juice in a separate bowl. Set aside.
In a large bowl, cream butter and sugar together until light and fluffy. Add orange zest and mix well. Alternately add flour mixture and juice mixture, beginning and ending with dries.
Gently fold in beaten egg whites and spread into two, well-greased or parchment-lined 8-inch cake pans. Bake at 350 degrees for approximately 25 minutes, or until center springs back when touched. Cool completely, and cut each layer in half horizontally. Can make a day ahead and refrigerate.