You are not giving enough information.
You say he hooked it up to city water. there are two water inlets. One is for the fresh water tank and the other is your normal city water inlet which supplies city water pressure directly to your piping system.
In order for your fresh water tank to run, you must have the pump switch turned on
If your carpet is soaking wet you either have a broken pipe someplace, your toilet overflowed, or one someone let a sink overflow.
If your fresh water tank over flowed it would go out the overflow and onto the ground . It wouldn't get on your carpet.
If the water situation is real bad, then the insulation under your floor must be wet too, and that can lead to a bad mold problem.
You should call a mobile repair service if there is no one else that can help you
Guy