I'd recommend finding a giant cave or similar where they've stolen a lot of booze over the years, and fill your waterskins there. But then again, I usually play adventure mode as a dwarf.
The times I've explored underground the biggest problem was getting tired and needing to sleep... you can get pretty unlucky there, even if it seems pretty safe.
I think if you take 3 or 4 full waterskins you should eventually run into flooded areas before you die of dehydration. Well, you're more likely to die of boredom or something vicious first, anyway
You can probably fill the waterskins from the pools of blood of your victims too, but I'm not 100% sure if that's drinkable.
you can tan skins from animals, (other things too but it's a bit buggy, you just get 'leather') and use them to sew yourself more waterskins, quivers, and backpacks... but you also need to gather plants to weave the threads to sew them, and also for bowstrings for making bows and crossbows. You can make bone bows, crossbows and bolts/arrows if you want to train the skills up, you'd probably want to grab bronze weapons and ammo to actually kill stuff though.
I'm not sure how well the game treats the properties of the bone/teeth you use to make the arrowheads when calculating penetration/damage, it's possible you could make a really awesome spear or arrow out of dragon teeth if you killed one, but I can't remember if that's been implemented, successfully modded in, or just a wishlist item. I honestly don't use ranged weapons much myself, I like axes.
Oh. Also, I play deon's genesis mod when adventuring. I don't know if you can do all that crafting in vanilla, haven't tried it.