The above advice is good. Let me put it another way:
You will be able to get water from gas stations and other establishments most of the time. So the question of how much water to carry is really a question you will look at on a daily basis, after considering the route map, the weather, and the amenities on the road ahead of you.
If you have places to carry three water bottles on your bike, and an empty water bladder or something in your pack that you can fill up when needed, you will have the tools you'll need. And of course you could buy some bottled water if you need to in advance of a dry stretch, and stash that in your packs or on your rack. Most of these bottles will also work fine in your bike's bottle cages -- use them a while, then recycle them.
I think that, most of the time, you will top up at least two of your frame-mounted bottles every chance you get.
The rest will work itself out during the trip.