Water in the basement ceiling..... That's one big mystery....

[George P.]

So so weird....

The tenant calls about a month ago saying the ceiling in the basement is dripping water o_O. He did shut the water down to prevent further damage.

We rush there, open up the ceiling, drain all the water (collected good couple of gallons), make three holes (big enough to stick a head and look around) but find no source of leakage! Opened the water supply again - NOTHING is leaking ! o_O.... I mean you can see the water on the sheetrock, but you just don't see where it WAS coming from. 

It's been a month, and no other water has leaked - we left the holes open hoping it would leak again so we can identify the source.... Nothing !....

The kitchen is right above it, checked all the appliances (including the fridge with the ice maker), under the sink - all is dry there .... Double checked the ice maker - it's still making the ice.... 

BTW It's been one of those very cold weeks on the East Coast (zero-ish degrees) The outside spigots have been "winterized". No loss of water pressure, no loss of water anywhere in the house have been identified....

Any ideas as to what else we could check?...... Don't want to drywall the ceiling before getting to the root of this mystery.... 

BEFORE we opened the ceiling: