Put 1 cup ice in a cocktail shaker. Add juice concentrate, lime leaf, lime juice; shake well to blend. Strain into 2 martini glasses, dividing evenly. Top each glass with 2 tbsp. soda water. Serve with a lime wedge as garnish.
If you like, make this drink with other juices—passion fruit, orange juice, or guava-guava—for a colorful mix.