In a 1-1/2-quart pitcher stir together the water, lemon juice, and sugar until sugar is dissolved. Place half of the undrained chilled peach slices in a blender or food processor container with 1 cup of the lemonade. Cover; blend or process until smooth. If desired, chill. Serve over ice cubes. Repeat with remaining peaches and 1 cup lemonade. (Refrigerate remaining lemonade for another use.) If desired, garnish with peach or nectarine slices. Makes 4 (8-ounce) servings.