Bring water to a boil in a medium pot. Stir in sorrel, ginger, cloves, peppercorns and cinnamon sticks. Turn off heat. Let cool completely in the pot, about 45 minutes. Transfer to the refrigerator to steep for 12 to 24 hours.
Strain the steeped mixture through a fine-mesh strainer into a large jar. Press the solids with a spatula to squeeze out all the liquid (discard solids). Add brown sugar; stir until completely dissolved.
Fill a 16-ounce cocktail glass with ice. Add 1/2 cup of the sorrel mixture. Top with 1/2 cup seltzer; stir. Repeat with the remaining ingredients to make a total of 8 mocktails. Garnish with orange slices, if desired.
Recipe Notes
Dried Jamaican sorrel, also known as hibiscus, adds tart-fruitiness and a gorgeous red-purple hue to dishes. Find it, such as Angel brand, online at Amazon.