Hi, Jaynee!
I'm thrilled to hear that you're finding so many helpful answers here on the Moms Panel! We all really enjoy helping Guests make the most out of their vacations!
While I have not seen entire cases of bottled water for sale at
Jackson Square Gifts & Desires, you can certainly ask a Cast Member if you're able to purchase a whole case. I'm sure that wouldn't be an issue, but it could prove to be cost prohibitive.
We love using Garden Grocer for grocery deliveries, but since you're just looking for the water, I have another suggestion you could try. Amazon.com has a grocery section where you can purchase a case of water and have it shipped to your Walt Disney World Resort hotel. I find that it's more expensive than buying it at home, but less expensive than buying individual bottles in the Parks. If you are an Amazon Prime member, you will save on shipping costs too! When you ship to Resort hotel, just be sure to put "hold for Guest" with your name and check-in date so the package will be there for you upon your arrival. You don't want to have the package arrive more than a day or two before your check-in date.
I hope this helps, Jaynee! Please let us know if we can assist with any other questions you have.
Wishing you and your family a Pixie Dusted vacation!
~Jackie