Week 3 water cannon
That water cannon was way too powerful. I can't think of any real world scenerio where their shelter could expect to encounter a force that strong that could also be survivable given the rules of the challenge.
Perhaps a tidal wave could be that powerful, but if anyone was to be struck by a tidal wave in either shelter, even if the shelter withstood the force, the occupant is now underwater with only minutes to live.
The water cannon should have been dialed back significantly to real world levels if they were designing a challenge that was actually achievable.