Preheat oven to 350°F. Line standard muffin pan with baking cups. In large bowl, combine cake mix, water, oil and egg whites; beat with electric mixer 2 minutes. Add lemon zest and juice; mix until well blended. Spoon into baking cups. Bake 20-22 minutes or until toothpick inserted comes out clean. Cool cupcakes in pan on cooling rack for 5-8 minutes. Remove cupcakes from pan; cool completely.