I have a small drinking bottle (0.4lt) attatched to the shoulder strap, and all the other bottles rest inside the pack, maybe if I had to carry 6 or more bottles (1.5lt each) I would strap two of them by the side straps to the outside of the pack.
That makes for a heavy pack and I have to take a short rest every hour or so anyway, where I take off the pack and can refill the small drinking bottle, if needed.
But usually I let myself drop into (slight) dehydration during hiking, I'm not a fan of sipping every few minutes.
Usually I measure my hydration state by the number of bathroom breaks, and the amount and color of pee. There is not much sense in drinking more than absolutely essential, just to drain it out an hour later.
I would camel up at the next supply point.