@sunnyVoid: [
ref] It is less that you don't
have water, than that you don't
want water, this is a normal side effect of some of these poisons --they mess with the bodies regulation-- and
Dirk may well have experience this if he has been --or encountered others who were-- poisoned or having sunstroke (heatstroke, or even just heat exhaustion, which I mention since they are the more likely places this will have been experienced) in the past.
But there was only a finite amount of drinking water with the party. Maybe If you want to roll the Die of Fate to see if we have any left in our canteens?
The poisoning is mainly a narrative consequence, so it does not have to stop you from doing any anything you want to do, but may flavour the negative outcomes. Include it in your descriptions as much as you like.