In doubling a squash soup recipe, I've got all the ingredients in the pot except for the doubled amount of liquids (broth and water). I wonder whether I can wait to add the remaining 5 cups of liquid until I reheat before serving, or should I add it during the overnight storage of the soup? Or should I divide what I've got so far and add the remaining liquid and heat it up before storing? My concern is for the flavor melding aspect.
You should be fine adding the water whenever it's convenient, as long as there's enough water in it already that you were able to cook it properly (and purée if necessary and so on). You're basically just making concentrated soup just like what gets put into lots of cans; water will mix in just fine.