Wet coming up on hardwood

was it built on a graveyard?

in general no, once something dries, it can't get reconstituted without an additional water source.

what kind of smell does it have?

That spot, carpet or not, may be some animal's place to urinate. If there is no water source above or near that spot, for it to have leaked there, then some animal returns to the spot, when no one is there (at night?), and does its thing.

To determine if it's a cat, tear up tissue paper (lots of small bits) and scatter it all around the spot. A cat will "collect" the tissue, when done, to cover up its business.

Sonny

Could water be leaking from windows/walls and running along the base of the wals, or studs and collecting on the sub-floor? Just a random thought...

You may also want to look outside for gutters and down drain pipes. Sometimes if not properly tilted the rainwater can backup and pass the flashing and get behind the siding finding its way to an interior wall where it could leak under a floor then wick up. Its worth a look anyway.

Where is the nearest sewer pipe, drain pipe, shower, tub, lavatory, kitchen= or toilet? If there is an access door like for a shower drain then turn on= the shower and check with flashlight or you may have to start making holes= in the walls until you find it.

Esp. in wintertime with ice and freeze-thaw cycles....

As urine dries it forms alkaline salts. Those salts are hygroscopic which means they suck up moisture from the atmosphare.

X-No-Archive: Yes

You could try to eliminate the above or below guesswork. Put a pan on the floor and see if it collects inside or out. I had an issue with a shower that accumulated water on the floor. Caulked the shower silly and it still leaked. Put down a baking pan one day and low and behold the water was under the pan. Turned out that it was leaking from under the floor where the drain connected. It sounds like you may have a pipe leak though.

Michael Lalonde ( Sudbury, Ontario ) Jumlers.com