Fill 2 pint-size glasses with ice. In a large metal shaker, muddle 12 mint leaves, 1/2 cucumber sliced into thin rounds, and a small scoop of ice. Add the juice of 1 lime, 1/2 cup coconut water (which naturally contains salt), and 1/2 cup watermelon juice. Cover tightly, and shake vigorously for 30 seconds. Strain into prepared glasses, and top each with 1/2 cup sparkling water. Garnish with more mint leaves and a cucumber slice.
Recipe by Carly Knowles, R.D.N., the author of The Nutritionist's Kitchen.