I have an older house (1920s) it's two stories, although the second story was probably the attic originally. I used to live in it, but now I rent it and live nearby.

There is a pipe that sticks out the side, and water drips out of it sometimes. It's at about the height of the the floor/ceiling between the levels, and close to the upstairs bathroom. It's PVC or some other non-metal material.

I never really noticed it until this winter when water started coming out of it at a steady trickle sometimes. It seemed to be related to the rain. I don't know if this was happening before or not. I thought maybe there was a drain up there that drains out of this mystery pipe (The roof is steep and it has dormers and chimney, so it's hard to get a good look at all parts of it). However, during the last month or so it started to have more water come out - a few gallons a day or more.

How can I tell what the source of the water is from this pipe? The location makes it difficult to cut holes into the drywall from the inside. Is there any other option or do I need to get some sort of professional to figure it out? I'm not even sure who to call.

  • This sounds a lot like a condensate drain for an HVAC that's installed in the attic. If so, it's doing it's job.
    – BMitch
    Commented May 20, 2016 at 23:21

1 Answer 1


Check all the tanks that hold water - they will have overflows in case of overpressure or in case an old fill-valve starts to fail to close completely.

If the plumbing system has header tanks for cold and/or hot-water, these have overflows for when the fill-valve gets old and fails to close completely. Also lavatory cisterns have overflows for the same reason.

Water heaters that work with a pressurised supply also have pressure relief valves to vent excess pressure.

All of these can either vent to the outside or to an internal drain.

So I would ask someone to watch the outside pipe while I go around and cause water to come out of each overflow/vent one by one. In lavatory cisterns you can probably hold a float-valve underwater to cause the water to rise above the entrance of the overflow pipe.

It's quite likely to be a lavatory cistern. A slow "leak" on the fill valve won't cause a problem if the toilet is in regular use. It's only when it hasn't been flushed for a long time that the "leak" can cause the level in the tank to eventually reach the overflow level.

  • Would it be a bad assumption that a header tank would be visible somewhere and not hidden in the wall or the attic space? :)
    – Adam Porad
    Commented Apr 28, 2015 at 21:35
  • 1
    Header tanks are very likely to be hidden in attic space, that is the normal place for them in my part of the world. They have to be well above the highest shower-head or tap etc. So when an attic is converted to living space, any header tanks in it either have to be raised up higher into the roof-space or the plumbing system has to be converted to a mains-pressurised system. Commented Apr 29, 2015 at 8:42
  • Update. It turned not to be a header tank but a full size water heater that was leaking. It was walled in between the bathroom and some "empty" space used for storage when the attic was finished. The drain pan was connected directly to the pipe going outside. We couldn't remove the water heater through the studs, so we drained and disconnected it and had a plumber install new pipes to bypass the water heater. The water heater is still there, and probably will be as forever :) The funny thing is even without the 2nd water heater, it doesn't take long for the upstairs bathroom to get hot water.
    – Adam Porad
    Commented Sep 25, 2015 at 19:19

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