How to Make It
Fill a 3-quart pot three-quarters full of water and bring to a boil. Using tongs, carefully set the jars on their sides, along with their lids and a long-handled, slotted metal spoon, in the boiling water to sterilize. Boil for 15 minutes, then remove from the water with tongs or a jar lifter and set aside.
Scoop the flesh from the watermelon and reserve for another use. With a vegetable peeler or a knife, peel the thick green skin from the watermelon rind and discard. Cut the rind roughly into ½-inch dice. You should have about 8 cups.
Place the diced rind in a 3-quart pot and add the lemon juice, water, sugar, ginger, and lemon peel. Cover and bring to a boil over high heat, stirring a few times to distribute the ingredients evenly and help dissolve the sugar. Reduce the heat to low and simmer, covered, over medium low heat for 40 minutes, or until the watermelon rind is translucent.
With the slotted spoon, transfer the pieces of rind to the jars, and leave the syrup to simmer and thicken for 10 minute more. Carefully pour the syrup into the jars (using a funnel, if necessary) until it is ½ inch from the rim. Place the lids on the jars, seal, and set aside to cool. Refrigerate for 2 days before using. The preserves will keep for about 4 weeks in the refrigerator.