Where are you staying??? When I'm at BW, I just walk across the street to the Hess Station and grab water there.
Or, you can use a grocery delivery service, but they will also charge you a fee.
While I understand that it's a lot cheaper to get a case of bottled water vs buying it bottle by bottle through Disney, I just can't see going to a ton of trouble to save a few dollars. But, then again, I'm at BW, so can just hoof it across the street.