On average plan on a mile and a half for the first half of the race then once a mile. As an approximate go by the half stops have been located near mile points 1.6, 3.5, 4.2, 6.3, 7.1, 9, 10, 11 and 12.5
Here is a mp with approximate locations.
http://www.mapmyrun.com/routes/fullscreen/4106815/
Note the irregular spacing is purely a factor of keeping cups out of the park and ease of supply.
If you feel you need supplemental water, then by all means train and plan on bringing your own bottle. I run with a bottle for the first half of the race. I start by sipping the contents while waiting for the start and it usually empress in the first 4-5 miles.
If it helps ease you mind some, you will not need the sip effect once winter kicks in. The feel for needing to sip is a cooling need as much as hydration. That feeling will diminish.