I was having the same question and finially I found out
on these DisBoards that you can go to DTD and walk across
the Street to Hess Gas Station and buy a Case of water
for around $6.00 a case so that's what we are going to
do. So I won't have to bother with trying to figure out
how to pack them in a check in suitcase.
Just bring an empty backpack or rolling suitcase with you to
DTD and this makes it easier to carry.
We will be staying at POR which has a Boat to DTD
but all resorts have a bus that can take you there.
This is what I found out on the Disboards:
Hess STation is across the Street from DTD West Side.
There is a Large Crosswalk at the section because there
is a Cast Member Parking lot, behind the Station.
Takes about 5 Min. to walk there from Planet Hollywood.
Problem Solved!!