You mean like a CamelBak? That's what the Army issues now in lieu of canteens...
It's basically a backpack water bladder with a hose you run around to you helmet, bite on it to open the valve and suck to get hydrated (That sentence sounded a lot dirtier than it is

)
Personally I just use a Drink Butler handlebar mounted mug on my bikes, just never been a fan of the backpack hydration solutions, although I hear they work great.
Edit to add - I queried the soldiers in my life, was told they love their CamelBak and the only con is you have to be careful to not leave it wet and let it fully dry out after usage to avoid mold...