crazyladyof5 - I agree the water in FL will be a shocker to you, it really tastes awful, especially warm (one of the fountains at WDW made me want to spit it out it was terrible).
Anyway, we drive down too.
I have gone to my local Sam's club or anywhere really that sells a 24 pk of waterbottles of our favorite brand. I believe I paid $6.97 a case for each, I bought two and put them in the back of our Expedition to take with us. We also bought a small plug in cooler to keep drinks and sandwiches in for the drive.
At night at our resort, we'd freeze some for the parks the next day. As they'd thaw, it was always a great ice cold drink. I put my DH's and mine in our backpacks and I bought insulated water bottle holders with straps at CVS for the kids, they slung it across their shoulders and had it immediately available to them.
The rest of the bottles always remained in the fridge. If you buy a couple of gallons for HIFS, it might take up all the room in the mini fridge, you could replenish the bottles as needed....just a thought...
Have a great time!