I'm looking for some BP brainstorming to help me properly address a recent maintenance issue in one of my rentals.

It's a 3/2 SFR concrete block on a slab, it has a glue down wood floor throughout the home. The tenant is a single Mom with 3 teenage/preteen age daughters so there is obviously a lot of bathroom use, but nothing that seems to be negligent or outside what it should be.

There is a hallway with 2 bedrooms coming off of the right hand side and the 2 baths behind the left wall with the master bedroom at the end of the hallway. The PM went by to look at some wood flooring that was "coming up", thinking it would just be a few spots that needed to be repaired. It turns out that it is almost the entire hall and extends into each of the bedroom doorways. So the flooring will need to be completely replaced, but the real issue is moisture causing the wood to swell and "pop loose".

The left hand wall where the baths are has a higher moisture content along the baseboard, and the wall between the 2 baths also had a high moisture content. Today the plumber went by and inspected and couldn't identify any active leaks in either the supply or drain lines or around any of the tub drains. He filled and drained tubs, ran shower heads, cut several inspection holes in the wall to see any active moisture and checked the vent pipe to see if it was leaking around the stack exiting the roof and found nothing. He did however say that in looking through his inspection holes it was "humid" under the tub area...but no leak. The wall cavity itself was not wet at all, but did seem that there may have been moisture in it at some point in the not too distant past and did read a higher than normal moisture content.

So before I feel comfortable having the floor replaced I'd like to identify the source of this, but do need to do it soon as it is not in a condition that I can just leave it as is for several weeks. This is where you come in, I can have someone else inspect other areas but can't for the life of me think of where the problem could be coming from.

So any creative ideas of other items to look at for a possible source of the water?