1 cup dried hibiscus petals
1 cinnamon stick
1 whole clove
1 whole allspice berry
⅛ teaspoon freshly grated nutmeg
1 ½ cups raw sugar
ice cubes
2 ½ (32 ounce) bottles sparkling water
2 limes, cut into wedges
Combine water, hibiscus petals, cinnamon, clove, allspice, and nutmeg in a medium pot. Bring to a boil over high heat. Reduce heat and simmer for 1 1/2 hours. Remove from heat and stir in sugar until dissolved, about 1 minute. Cool syrup to room temperature, about 1 hour. Refrigerate until ready to use. Make hibiscus coolers by filling 10 glasses with ice. Pour 3 fluid ounces hibiscus syrup into each glass; top with 8 fluid ounces sparkling water. Squeeze 1 lime wedge into each glass.