We are on a ground floor of a condo building and to put up the partitions I drilled a small hole and after about 1" depth the drill fell into a void (about 1" more) and about a quart or so of clear water came out and stopped.

What could this be?

The drain pipes in the building are cast iron and visibly enter into our unit so this doesn't seem to be plumbing. The concrete slab is 10".

  • 1
    I'm posting this as a comment because it's not really an official answer but that has to be waste/drainage of some sort, anything on the supply side would have been pressurized and you'd have water shooting out. Maybe a p-trap or something. Or...if you're really lucky, maybe somebody dropped a bottle of water in the slab when they were pouring it. That is a long shot though.
    – user23534
    Sep 10, 2014 at 22:44
  • Too late now, but if it's a condo, you usually can't go drilling into shared walls/ceilings without permission.
    – DA01
    Sep 11, 2014 at 3:44
  • @Paperstreet it's a commercial unit so the drains are cast iron and my Masonary drill bit wouldn't go into them. Besides they all run straight down into our unit and don't go horizontal in the slab.
    – MandoMando
    Sep 11, 2014 at 14:09
  • Maybe condensate line or a drip pan from the HVAC system.
    – user23752
    Sep 11, 2014 at 16:43

1 Answer 1


Void spaces are frequently used for utilities, it could be accumulated condensation. Leave it be and see if more water comes out to find out if it's an active leak. I hope you did not drill through an HVAC line or drain line.

  • I doubt it's a drain line since they are cast iron, big and run vertically into our unit and visible before going horizontal. Not hvac either since I see those as well. The only thing I can guess is a conduit for the wired CO detector nearby. But water in that conduit?
    – MandoMando
    Sep 11, 2014 at 14:11

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