Using a metal spoon, scrape the rind to remove all traces of pink.
Using a sharp peeler, remove and discard the exterior green portion of the rind.
Cut the rind into 1 inch cubes.
Add the water, sugar, apple cider vinegar, ginger, salt, red pepper flakes, allspice berries and star anise to a pot and bring to a boil over medium high heat.
Cook for one minute.
Add the watermelon rind and return to a boil.
Remove from the heat and cool for 30 minutes.
Transfer to a glass jars and keep sealed in the refrigerator for up to 2 weeks.