Cut watermelon rind into 2-inch long, 1-inch wide, and 1/2-inch thick pieces.
Combine water, sugar, spearmint, and basil in a large pot. Bring to a rolling boil. Strain out spearmint and basil. Add watermelon rind, making sure pieces are completely immersed. Cook until rind is soft, about 5 minutes.
Drain watermelon pieces and arrange in a single layer on dehydrator trays. Dry according to the manufacturer's instructions until pieces are candied, 6 to 8 hours.