Basement water source mystery

October 18, 2009 11:57 PM

How is water getting into my basement?

I discovered a substantial amount (~20-30 gallons) of water in a puddle in my basement. I haven't been in the basement in a week, so there might have been more, and it either went down the drain or evaporated.

I figure the water may be coming from seepage through a hidden crack in the wall, from the basement drain (which is near the puddle), or from the water main.

It's been raining a lot here lately, which points to seepage. But the walls and floor don't have any visible cracks, and the walls are completely dry.

The water main is suspiciously near the puddle, and looks old and corroded (green). It's even slightly damp on the outside. But it isn't actively leaking.

The basement drain is also near the puddle. Can seemingly clean water come out of a sewer drain when it rains?

We don't have gutters, so it's not a gutter issue.

Should I call a plumber for the water main, for the drain, pile up more dirt against the outside wall, or just live with it?

Thanks! This is really bothering me.

posted by miyabo to home & garden (14 comments total)

It could be due to any source you've listed, but given that you say

"... It's been raining a lot here lately, which points to seepage. But the walls and floor don't have any visible cracks, and the walls are completely dry. ..."

and

"... We don't have gutters, so it's not a gutter issue. ..."

I'll venture that it most likely a backup of the floor drain from the sewer, under heavy rainfall conditions. More and more cities are working to separate storm water runoff systems from sewer systems, but still, in many areas, a combined system handles both stormwater runoff and sewage. This is bad, if you get very heavy rainfall, as the water levels in the combined sewers get high enough to back up, and the combined sewage/stormwater is still pretty nasty. It's also possible that, without gutters on your house to direct roof runoff away from your foundation, that you simultaneously got a lot of water saturating the ground around your basement, and even coming up through the floor drain. But it doesn't take a very big leak in your basement waterproofing to put a lot of water in your basement in a hurry. A hole of only 1/4" diameter may "only" flow .004 gallons per minute (from an unpressurized source, at a leisurely 1 foot per minute of flow), but even that's still about a quart of water an hour, from a nearly invisible leak in your basement walls or floor. A 1/4" hole, under greater pressure, can leak 4 to 5 times that rate, easily.

You probably can't learn much from the waste water left in your basement, because a rush of storm water, backing up in sewer line that isn't already full of sewage, can appear pretty clean. I'd call a plumber to check the source of the water (using dyes and maybe a video snake), and make recommendations. The last thing you need is raw sewage, even diluted with stormwater, filling your basement.
posted by paulsc at 12:42 AM on October 19

To rule out the water main, stick an old towel over it and see how much water it collects. I have encountered pipes that just looked corroded and I found that they were all corrosion and there was no metal left.

I think that it is more likely you drain though. Also if it is dry around the perimeter of the puddle, you can put some sand or sawdust around it and then you can see which direction it was flowing from. Provided it does it again.
posted by psycho-alchemy at 1:19 AM on October 19

Sprinkle talcum powder around any suspicious places, and next time it leaks, you'll have a clear view of where the water is coming from. This is reliant on you getting talc around the source of the leak, obviously.
posted by Solomon at 4:55 AM on October 19

It is possible that -- depending on how thin your slab is, how high your water table is, and many other unrelated bits -- water can just bubble up right on through the concrete. Concrete is porus, and hydrostatic pressure is ridiculously strong. I think it's more likely a drain, since I'm convinced I have the freak water house of doom (where water tends to bubble up through the concrete just to spite me), but it's a possibility.
posted by Geckwoistmeinauto at 5:20 AM on October 19

Put a bucket under the overflow valve in your hot water tank to see if that's the problem.
If it is, the pressure is too high, and your main pressure reducing valve needs replacing.
posted by weapons-grade pandemonium at 5:26 AM on October 19

The basement drain is also near the puddle.

Basement drain as in floor drain or basement drain as in the cleanout for your sewer connection?

We don't have gutters, so it's not a gutter issue.

I'd agree with paulsc in that it's probably a gutter issue because you don't have gutters. Directing water away from your house cures a lot of leaky basement problems.
posted by electroboy at 5:47 AM on October 19

With that amount of water really the only thing that makes sense is back-up out of the drain. That amount of water coming from the main would require noticeable dripping. It also seems to be too much to seep through intact concrete. It could be that one of your drain pipes has been compromised by tree roots which can block or partiall block the drain and also allow ground water to enter the drain. When the quantity is high enough and the blockage sufficient it backs up into the house. If it was a problem with co-mingled storm and wastewater sewers then some of your neighbors might have had problems as well. You might ask.
posted by caddis at 7:07 AM on October 19

Two things: it probably collects near the drain because of the slope of the floor.

Or, it could be bubbling up from underneath, through the joint between the drain pipe and the floor slab.

And, even though the city waste water systems might be combined, chances are quite good that they aren't inside your house or even all the way out to the street. You could have a situation where you are having a sewer backup just inside your own system. Maybe even a break in the pipe somewhere between the house and the street that allows ground water to seep back into the house, where normal waste flows fine.
posted by gjc at 7:14 AM on October 19

Water in a basement will collect near the drain, because the drain is essentially downhill. Yes clean water can come up through the drain or more likely the sump if you have one. However, we had mystery water in our basement which we finally fixed by getting our roof gutters repaired. They weren't doing their job directing the run off from the roof to the downspouts, so even though our basement walls were solid, they couldn't handle the large volume of water pouring off the roof during rainstorms. Fixing the gutter fixed the problem, without any repair to the walls.
posted by nax at 7:48 AM on October 19

An easy way to test whether you have a sewer service line blockage is to run your washing machine. They use the most water of any of your appliances, and have a high flow rate when it discharges. If you don't see a backup, chances are it's not the sewer. If you want to be really sure, have a plumber scope it. That said, it doesn't sound like your sewer is the problem.
posted by electroboy at 8:01 AM on October 19

IF you dont have gutters thats a big big big problem.

Gutters keep the water from fallking off your roof and landing next to the side of your house. They move the water to a safe distance away.

I would seriously look into gutters for your house.

I know this because our gutters backed up and got deformed and the water fall over them as if there werent any gutters and our basement would gather watter when it rained hard. We fixed our gutters and the water went away.
posted by majortom1981 at 9:36 AM on October 19

You say the walls and floors don't have any visible cracks. Could there be a crack at a corner where two walls meet? It might be hard to see.

Your water main being green might be because of condensation. If that was where the leak is, You'd probably see it dripping or leaking.

I recently had water in my basement. I found it was coming from the roof. The water was leaking through the roof, running along the trusses in the attic to the outside wall of the house. Then down the outside wall into the basement. But I could see it coming down the basement wall when it rained.

What about a window leaking ( not sealed) and then the rain running down a wall into the basement?

Seconding marjortom1981 about gutters though. We call them eaves troughs and downspouts. But that very well might be the problem. They keep the water from soaking the ground immediately close to the building and direct it away from the foundation. Most houses have the land surrounding it sloping away for drainage. Otherwise the water could saturate the ground and seep into the foundation if theres too much water.
posted by Taurid at 11:22 PM on October 19

Thanks everyone! I had to wait for another heavy rain to be sure, but it did turn out to be the leaky corroded water main. That said, I'll definitely look in to adding gutters/improving the slope away from the house.
posted by miyabo at 2:39 PM on October 21

Correction: it was the water main AND the sewer, at the same time. Too bad plumbers don't offer bulk discounts.
posted by miyabo at 12:03 PM on October 30