Cut 8 very thin wedges from apple; core, peel and roughly chop the rest.
Toss the apple wedges with 1/2 teaspoon of the lemon juice in a small bowl.
In a separate small bowl, toss chopped apple with the remaining 1/2 teaspoon lemon juice.
Puree chopped apples, 3 tablespoons ice water, and Stevia (sugar substitute) in a blender.
Divide pureed apple mixture among 4 glasses (about 2 tablespoons each); top each with a few ice cubes and fill each glass with seltzer.
Stir, top each spritzer with 2 apple wedges, and serve.
Each drink is 3/4 cup.
Source: South Beach Diet