Most of the fluids they take in comes from their food. That's one reason I don't make my feeders completely dry after warming them in water, its like food and drink combo.
Just as our skin can get dry, so can theirs. That's why they need the humidity to be correct because other wise they get dry skin and then we all know what happens. But high humidity or soaking does not provide them fluids the same as drinking does. They still need to drink. If they didn't we wouldn't need water bowls.