Bring 4 cups of water to a boil in a medium saucepan. Add the hibiscus flowers, agave syrup and lime zest and let steep 7 to 10 minutes.
Strain through a sieve into a pitcher, discarding the solids. Add the lime juice, 2 cups cold water and 2 cups ice. Serve over ice and garnish with lime.
Recipe courtesy of Guy Fieri for Food Network Magazine