If you have a whole turkey with giblets, you simmer the giblets the day before with onion and a bit of sage plus other veg if you like -makes a lovely stock. Then make gravy in the roasting tin in the usual way - no need for veg water.
If you rest the turkey for an hour, the gravy can be made once it’s out of the oven - pour into a small saucepan, no last minute faff.