How to Make It
Press the cucumber slice against the inside of a chilled highball glass and add ice. In a cocktail shaker, muddle the chopped dill, agave syrup, lemon and lime juices and 1 tablespoon of water until the syrup is dissolved. Add ice, then add the cucumber juice and shake well. Strain into the prepared glass and stir in the club soda. Garnish with the dill sprig.
Cucumber juice is available at juice counters. You can also make it by pureeing peeled cucumber chunks in a blender and then straining the puree through a fine sieve. One large cucumber yields about 3/4 cup of strained juice.