Water in basement... baffled... seems plumbing related
I have had a problem for several months with a ton of water in the basement... I think I finally narrowed it down to a plumbing issue as it was perfectly dry and then I ran a load of dishes through the dishwasher on a perfectly dry day and I have at least 30 gallons on my basement floor. The problem is I have never seen any leaks anywhere... there is no evidence of any drain lines leaking. I pulled out the dishwasher and it is dry underneath.
This is a house with a full basement all the plumbing pretty much is in the floor joist cavities 8 feet above the basement floor and totally exposed... so any leak there should be fairly loud and obvious. The septic line exit and cleanout is also a couple feet above the floor.
There is one drain in the floor and a sink that doesn't get used very much, but it must be plumbed differently as it obviously doesn't go out with the rest of the waste water... I'm assuming that connects in the yard 8' underground to the septic line further down the time. The water doesn't seem to be coming in through there anyway as the area is recessed a bit, dry, and on the other side of the house from where all the water is showing up.
Any ideas on how to find this? It is driving me crazy. I don't really want to pay a plumber just to stand around and be as baffled as I am... and I don't know what a plumber would do other than run the taps and look for leaks (which he won't find). I even filled the kitchen sink completely with water and let it all go at once, thinking maybe you just need a lot of volume to trigger it. I saw and heard nothing in the basement.
The only thing I can think is it is coming up through the (concrete poured) floor or where the floor meets the (block) walls... but it sure is coming in fast for that. And there's no swamp outside or any evidence of water pooling around the house... The septic also goes out the back of the house and all the water is in the front.
The water in the basement does not stink at all. It seems perfectly clean. Like a supply leak (except the supply lines would be pressurized all the time and it doesn't happen all the time so I have pretty much ruled that out on that basis). Any ideas?