1 Cup of Sugar
1 TBSP Lime Zest, plus one cup fresh Lime Juice
1/4 Cup fresh Basil Leaves, tightly packed
1 Medium Cucumber (English pref), halved and thinly sliced
2 Cups chilled Sparkling Water
 
In a small saucepan, bring the sugar, lime zest and 1 cup of water to a simmer over medium heat, stirring constantly until the sugar dissolves, about 6 minutes. Remove from the heat and stir in the basil leaves. Let cool for 30 minutes.
 
Strain the lime/basil syrup through a sieve into a pitcher. Add the cucumber + lime juice; refrigerate for at least 1 hour.

Just before serving, add the sparkling water. Serve over ice.