In a Dutch oven bring water, sugar, cider vinegar, gin, salt, mustard seeds, celery salt, crushed red pepper flakes, and bay leaves to a boil over medium-high heat.
Add onion, peaches, garlic, and jalapeno and boil, stirring occasionally, for 15 minutes.
Let mixture cool, and remove bay leaves. Relish can be stored in airtight containers in the refrigerator for up to 2 weeks. (Makes about 8 cups.)