I think that the pit would be the most likely to fill with water, as I had described Vror and Carl as having to walk down an underground sloping passage toward camp in order to get to the chamber on the other side of the wall from the pit. I do apologize for any confusion. I see it in my mind's eye and think I haven't written it as vividly as I see it.
Maybe some people might be in the pit trying to repair the plug or move the orcs out of there when it bursts? Another option could involve children getting lost in another underground passage, but I think the first might be the stronger of the two. No time to think, just have to act quickly, you know?