Carry enough water to get you to the next place you can get water. For me, that's usually two or three regular (big) bike waterbottles. If you need to have more with you, buy a couple of liters in a convenience store or whatever, re-use the bottles until you are past the long/dry stretch, and then recycle/throw away.

Carrying the bladder the whole way is just extra weight you don't need. I guess if you are free camping you might want more with you...

as for loading, the standard lore is 40% rear 60% front bags, but I always end up with more in the front. the side-to-side balance has to be pretty close in front, but doesn't matter so much in back. So it might be tricky to have a really heavy bladder in one front bag, you would have to balance something else really heavy on the other side, and then as you use the water, move stuff around so the sides are even. I usually carry food in front, and move it around between the sides as I consume it to keep things balanced.