Water bags don't grow on trees at base, so you can't gather them as many as you want. Of course there're wells in guarded towns, but if water bags could remove CD for gathering, then wells in towns can be removed, may be only wells in unguarded towns or random encounters near popular towns and you'll get crafting or science or any other CD (which can't be removed with using water bag) while filling bag with water, so you can't make 50 water bags at once. So you'll have to fill 1 water bag, then wait some time, then again, and then some russian PK with russian mercs could come and kill you.