Trim the pink flesh and the green outer skin from the watermelon rind.
Cut rind into small pieces, about 1" x 2" and measure out about 8 cups.
Put the rind into a large, nonreactive container and cover with brine made by combining 3 quarts of the filtered water and the sea salt. Refrigerate overnight.
In a saucepan, cover the watermelon rinds with the brine water and simmer until just fork-tender, about another 10 minutes. (Pay attention - Overcooking will cause the rinds to become rubbery.) Drain thoroughly.
Meanwhile, in a separate saucepan, combine sugar, vinegar, 1 cup water and spices. Bring to a boil, lower heat and simmer for 15 minutes, then add the cooked watermelon rinds to the pan.
Simmer watermelon rinds in the syrup until they become translucent, about 30 minutes.
Pack the hot watermelon pickles and syrup into clean, hot pint or half-pint jars, leaving 1/2-inch headspace.
Wipe rims of jars with a dampened towel and apply two-piece metal canning lids. Without sealing, these pickles will last 2 weeks in the refrigerator.
To can and seal, submerge the full jars in boiling water (enough water so the jars are 1-2" below the surface); boil for 5 minutes (or slightly longer at higher altitudes).