I am ordering my water from Costco.com...
They have free shipping and you can have them deliver right to the resort and have them hold it until your arrival.. I believe 1 case is close to $7.. but that's including delivery. I'm not a member of Costco, so they add a surcharge. I think it was $.70 for 2 cases, so my total bill was about $15.. worth it in my opinion...
I was going to order extra snacks and breakfasts items, but then booked a fabulous deal with Southwest which allows for 2 free checked bags per person.. so I'm packing a whole suitcase full of food too!