Im a bit confused about this as well, but I never order water unless its free from the counter service. Disney will give me 4 free cups, straws, and lids, full of ice cold water; why would I want to buy it and lug it around???
The water at MK is a bit horrid, but nothing a Koolaid single or Crystal Lite single cant fix.
Just my opinion. We all have them.
On our trip last August we ordered in online from Staples and had it delivered. I can't remember what we paid but I know that it was cheap and we went through both cases.