There are over 12,000 hits on basement water in alt.home.repair. But I
couldn't find anything that quite matched up with what I'm facing.
We've had water appear in the basement guest room twice now. Once one
year ago, once last week. And I seem to have ruled out all possible
sources...so I must be overlooking something.

When the water appeared a year ago, it was so strange that we figured
one of our teens must have tried to empty the dehumidifier and spilled
it, though they swore they hadn't. But now the same thing has happened
and the dehumidifier isn't in that room.

FACTS:

1) The house is a raised bungalow, so the basement floor is only about
five feet below ground level. The guest room is in the corner of the
house opposite the main basement drain. It's also far away from the
city water line and any other water lines that we know of.
2) The water appeared centred about 4 feet from either wall, so wasn't
in a corner nor smack in the middle of the room. One of the
aforementioned walls is exterior, southeast side, the other is interior
and load-bearing.
3) On the other side of the interior wall is an unfinished work room
where we can check ceiling joists and see bare concrete block. Bone dry
in there.
4) After a couple of days (we found the water on Tuesday) the water had
spread in a circular pattern. We had a fan and the dehumidifier in
there by then.
5) Upon lifting the carpet and pad today, I was able to determine that
the apparent origin of the water is the local high point in the floor.
My carpenter's level says so, and pouring a bit of water on the floor
underneath shows that it all flows away from that point. Water poured
nearby will not flow up to that point.
6) The old floor is 40+-year-old asbestos tile, bonded down like
nobody's business.
7) No sign of water from the ceiling. The dining room is above the
guest room.
8) Our basement flooded (as did many people's) after torrential rains
in May 2000. I put in new drywall and made sure to have vapour
barriers, sealed joints between walls and floor, and venting of the air
space behind the drywall to fight condensation build-up behind the
walls, just in case. So I can easily check behind the walls. Dry, dry,
dry.
9) During the 2000 floods, our main problem was a crack in the concrete
in another area of the basement where a wall had been taken out,
probably by the original owners in the 60's. Hydrostatic pressure was
pushing water through the crack like a tiny geyser. We had the crack
repaired. We also had the downspouts rerouted to run out to the lawn,
at least 12 feet from the foundation, instead of into the weeping tile
system, which is 47 years old.
10) We're in the midst of the hottest and dryest summer on record here.

My theories a

A) Our kids are malicious liars.
B) The water came through the foundation walls, flowed uphill, dried
itself off the walls and the carpet through which it came, then flowed
back out from its rallying point.
C) We have hydrostatics troubling us again despite near-drought
conditions.

I am perplexed. What am I overlooking? What fundamental thing do I just
not understand?

Thanks for ANY ideas!