The one I bought platypus big zip holds 1.5 l which is fine for me. I drank before start and had fluid left at end. My body is happy me shoving a load of liquid and food in it before the start. Do this before road races as I often forget to eat in the madness of first hour, so used to it.
How much fluid does the bladder hold?
I'd normal drink 1-2L in a 100 I think, depending on ambient temp. ~500ml/hr