Divide jalapeño slices (if using) between 2 (16-ounce) glass jars with lids. Once cooled 30 minutes, divide watermelon rinds and pickling liquid between the jars. Cover and chill in the refrigerator for up to 2 weeks. For the best flavor, chill at least 24 hours before serving.
Substitute additional white vinegar for the rice vinegar if desired.
Pickling salt is an additive-free salt made with fine granules that dissolve easily in brine. Substitute kosher salt if desired.
This recipe originally appeared on GratefulGrazer.com.