Combine water and salt in a large glass, ceramic, or stainless steel container. Add squash and soak 1 hour. Drain squash, and rinse well.
Combine sugar, vinegar, and celery and mustard seeds in a stainless steel stockpot; stir well. Bring to a boil. Add squash and remaining ingredients. Return to a rolling boil; reduce heat, and cook 5 minutes, stirring frequently.
Quickly ladle relish into hot sterilized jars, leaving 1/2-inch head space. Remove air bubbles. Cover with metal lids, and screw bands tight. Process relish in boiling water-bath 15 minutes. Serve with meats and vegetables.