Bring the water to a boil in a medium size pot. Remove from the heat and add the hibiscus flowers, ginger, honey and mint leaves. Cover and let steep for 20 minutes. Strain into a blender and discard the used hibiscus flowers, ginger and mint. To the blender, add the the watermelon and lemon juice. Blend until smooth. Strain the mixture through a fine mesh strainer/sieve or into a bowl lined with cheesecloth. Squeeze out all the juice and discard the watermelon pulp. Pour the mixture among 8 popsicle molds. Place the molds in the freezer and freeze for 1 hour. Remove and insert popsicle sticks. Return to the freezer and freeze until firm, about 4 hours. To remove the popsicles run the mold under hot water for 10 seconds and then pull the popsicles out of the molds. Store in the freezer.