Leak Detection Help

Hi people,

I am looking for a little help here.

I have a spot in the master bedroom (next to the wall separating it from the master bathroom) that is getting wet. If I put down paper towels and some weight on top I might get a moist spot about the size of an apple. At another time, It might soak three layers of paper towels. We might go 5 or 6 days with not moisture whatsoever. We might go 3 or 4 days after the last rain with no moisture. I can run all of our indoor water utilities and it won't recreate the moisture. I can go 5 or 6 days without moisture, using all the utilities as per usual. Note that my house is on a slab.

Here are some questions:
1. I made sure none of our indoor or outdoor utilities were running. I then went out to the water meter and recorded the number, the position of the triangle, and the time. I watched the little triangle and it wasn't moving at all. After 30 minutes I re-checked it. The number had not changed and the triangle had not moved. I turned on the outdoor hose and saw that the triangle immediately started moving. Doesn't this mean that I DON'T have any leaking pipes?
2. I thought I might have water coming under the slab. Where the brick meets dirt I didn't notice any rodent holes or anything and I don't get standing water. Where the brick meets with concrete slabs (back porch, front porch, driveway) there is the usual material separating the house from the concrete. In a couple of places this material was worn and there were holes. I filled a few of these with self-leveling concrete crack filler – is that ok to use for this purpose? Note that I still had a water spot after plugging holes.
3. If it isn't a broken pipe then it must be coming from the roof or from under the slab. It is impossible for me to get to that area in my attic but I am going to do my best to try and make a path to that area so I can look during our next rain. Is there anything else I can be doing? I just don't notice anything around my slab. It is easy to get up on the roof, but I don't notice anything out of place there. I do have a vent stack in the area and the flashing isn't completely covered – should I perhaps put some kind of spray foam or something around this – what should I use?

Any advice would be most helpful. And by the way… if I have to pay someone to crawl into my impossibly tight attic and create a plywood path across two rooms…. What sort of estimated cost would I be looking at (Mississippi prices)?

My guess it's just the vent boot that's leaking. Happens all the time.
There now have a simple to install rain cap that simply slides over the vent pipe and covers the old dry rotted seal. If you can not find one you'll have to replace the whole roof vent seal. A flat bar, hammer, a few roofing nails is all you'll need. About a 1/2 hour job.

Thanks Joe - I will certainly look for one of those rain cap - as it will cost nothing resource wise. What do you think about my individual questions - am I making safe assumptions?

What kind of floor do you have in the bedroom and what fixture are on the bathroom side of the wall? A leak in the wax ring under toilet can allow water to travel under tile, make sure the toilet hasn't been sealed to the floor.

When my a/c evaporator drain stopped up it overflowed and dripped to the floor of the closet it was in, the water then ran under the carpet padding but didn't wick out to the carpet until it got to the middle of the hall Because the thin plastic layer on the padding had worn out in the high traffic area in the middle of the hall.

Thanks for helping everyone!
Here are some updates:

Area is nowhere near hvac

I finally got to the area in the attic (very difficult). Everything perfectly dry up there (and I waited until heavy rain to go up). No leaks. I also pulled the insulation up and looked at the actual ceiling around those areas - bone dry. There just isn't any water coming in anywhere. I also looked around the vent pipe - nothing.

I put a rain cap over my vent pipe just in case. No help - Still got spots.

So it isn't coming from the roof - that means that it is either something in the wall connecting to the bathroom or something from under the slab wicking up through a crack at the location.

Facts that make me think it is coming from under the foundation up through a crack – We don't get moisture on the spot every day. If it had anything to do with our bathroom plumbing I would expect moisture every day. Also, the water spot seems to be a few inches out from the wall connecting to the bathroom (not all the way against the wall).

However we do NOT use our second bathroom as regularly. This bathroom is in a different area in the house… but I was thinking that maybe it had pipes connecting to our bathroom. Note that outside at about the same place where we have the moisture, there are two pvc access points sticking out of the ground. They have screw off lids. What should those be and is it possible that one of those is leaking? Note that my meter is NOT running so I shouldn't have any leaks in my pressurized system. But maybe each bathroom's drain pipes run under the slab right there… and maybe there is a small crack in the drain pipe running from our second bathroom???

So is it time to pull up our bedroom carpet?
What do I assume if I see no cracks?
What should I assume if I see a crack?
How much should I expect to pay someone to restretch my carpet back into place later? Can I do that myself?

You can rent a carpet kicker, I would pull the carpet back and see what going on. I think you will find that it comming from the bathroom. You do need to dry the carpet and under lay asap.

Try just using the other bathroom for a few days and see what appears.
I'm guessing the 2 baths are on the same floor and there are no baths above?

The 2 access points outside are probably cleanouts for the waste lines.