Bring 1c sugar and 2 cups water to a simmer, and simmer for 1 minute. Remove from heat. Stir in hibiscus and lime zest, taking care to avoid the bitter lime pith. Allow to cool completely, then strain through a fine mesh sieve. Refrigerate.
Mix 1 part syrup, 2 parts soda water with fresh squeezed lime juice to taste. Serve chilled.