In the stampede scene we notice that the pelican who steals the game leave through a big hole in the wall! Later in the movie the whole house is flooded by a monsoon! What happened to the hole in the wall! How did the house get filled with water?
Well my take on it all is that if the game can do all these things including creating a stampede that put a hole in the wall, then if the game wants them to drown in an in-house monsoon, then it will do that and it will make it that it is possible to do that. So basically I rekon the game fixed the wall so they could drown.
If you remember correctly, when they left the house they showed a small clip of those killer plants growing on the wall. I think that these killer vines covered up the hole in the wall.
You do have a good point about the hole in the wall. But think about this, wasn't that strange vine/ivy stuff always growing thicker and stronger? Perhaps it covered the hole enough so that it could hold a lot of water inside the house, while only leaking a little through the holes.