I've used: MSR dromedary bags, Sea to Summit bag and Platypus. All seem to do what is necessary.

I've generally used combinations of smaller bags to load things up. For example, when cycling around Australia I carried up to 18L of water with the following "loading sequence":

- 3 bottles on bike = 2L
- camelbak = 3L, 5L total
- 2 normal water bottles in pannier = 3L, 8L total
- second bladder in camelbak = 3L, 11L total
- sea-to-summit bag = 4L, 15L total
- miscellaneous bottles bought and put in panniers = 3L, 18L total

On a different trip across Russia, my cycling partner had a 10L MSR bag and I had a 4L MSR bag. We used the 10L just for the last kilometers before camping. Worked well there, but I'd generally find a collection of many smaller bags worked better than one large 10L bag.