Sterilize four pint canning jars according to the manufacturer’s directions.
Stir together the water and salt in a large bowl until the salt has dissolved. Add the squash to the brine and soak it for 1 hour. Rinse the squash, drain it, and rinse and drain it again.
In a stockpot, bring the sugar, vinegar, celery seeds, and mustard seeds to a boil. Sti