If you can find a deep enough groundwater spring that seeps up, even in Florida it can get pretty cold. I've never tested the temperatures in them with a thermometer, but I've been to several that are so cold, if you swim in them for too long you'll start shivering and your extremeties will loose feeling, even in the height of a Florida summer! However, most of those tend to be very large springs, such as the ones at Silver Springs, and there's another that was made into a pool and is miserably cold, but I forget the name of it. I've even used shallow flowing creeks from a groundwater spring to keep a bottle of water refreshingly cold while I was out hiking.
Bottom line is that water maintains temperatures far longer than air or land...the deeper the water, the cooler it is. Still, for food storage, I'd want to test it with a thermometer inside a cooler, first. Unfortunately, the cooler will insulate very well against external temperature change. You might need to suspend the cooler underwater with the cooler open for a while, to get the plastic and insulation cold, then bring it up and put the food in it after emptying it, just to get the temperature down quicker.
Bottom line is that water maintains temperatures far longer than air or land...the deeper the water, the cooler it is. Still, for food storage, I'd want to test it with a thermometer inside a cooler, first. Unfortunately, the cooler will insulate very well against external temperature change. You might need to suspend the cooler underwater with the cooler open for a while, to get the plastic and insulation cold, then bring it up and put the food in it after emptying it, just to get the temperature down quicker.
