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Finding a mystery leak?
April 10, 2011 8:50 AM   Subscribe

My house gets its water from a well. I've been noticing the well pump running at odd times, even when water is not being used. As a test, I double checked that all faucets were off, no washer in use etc. Sure enough the gauge on the pressure tank was slowly dropping, at a rate of about 5psi/min. There is no visible leak anywhere. Any suggestions on how I track this down?

I also shut the valve to the well, and to the hot water tank. This did not stop the pressure drop so I've eliminated those as possibilities. If I shut the valve supplying the house cold water, the drop stops.

My house is on a concrete slab and there is no crawlspace or basement underneath. The pipes are well hidden somewhere (run through the slab?).

I am hopeful there is something simple I am overlooking...
posted by cosmac to Home & Garden (17 answers total) 3 users marked this as a favorite
Do you have a bladder tank? If so, it works by keeping everything pressurized. You should find an air release valve somewhere between the tank and the pump. Listen/observe carefully to see if any air is leaking out, like finding an airleak in an innertube. If it is leaking it causes the pump to turn on intermittently to regain pressure. The little valve can go bad and need replacing.
posted by M Edward at 9:08 AM on April 10, 2011

If I shut the valve supplying the house cold water, the drop stops.
So that's likely your answer.

[Otherwise I'd said it's likely the tank. They do fail sometimes. It could be the tank in any case, actually, or a combination of issues. What type do you have, a bladder tank, or a simple air pressure tank? If the latter, have you ever completely emptied and refilled it to replenish the air? Otherwise your pump will go bonkers; bad on the pump and irritating as hell. If the former, are you sure the diaphragm is still working? They can fail.]

Otherwise: double check all the toilets and faucets once more, with only the cold water valve open.

If you find no leaking washer/toilet, and your tank is good, there's possibly a leaking pipe somewhere.

Try to identify the channel where all the pipes come together and go down in the house toward the concrete slab (unless the house is only one floor high, obviously), try to eliminate any leak inside any vertical channels above slab level. If you find nothing, it's time for a plumber to take over. Or try find the drawings of your house so you know where to put, you know, your ear on top of the slab.
posted by Namlit at 9:11 AM on April 10, 2011

What type do you have, a bladder tank, or a simple air pressure tank?

It is a "Diaphragm well tank". However, since turning off the cold water feed stops the pressure loss, I don't think the tank is the issue. It seems to perform just fine otherwise.

Yes, the house is one story, with vaulted ceilings so my guess is the pipes are in the slab. Good suggestion on looking at the drawings, I actually do have some (house was built in '58). I've got a bad feeling about this...
posted by cosmac at 9:26 AM on April 10, 2011

Sometime, when copper pipe is buried in concrete, the copper is slowly eaten away by the concrete. But if this was the case, I'd wonder where the water is going. You've proved the pressure drop is on the cold water line, have you tried turning off each shutoff valve on the other end of the line, i.e. the toilet, sink, icemaker, ect? At least you can determine if the leak is in an appliance or the floor.
posted by Marky at 10:31 AM on April 10, 2011

where are you..?. if you're in a cold climate, it's very unlikely the plumbing is in the "slab"... You're sure there's no crawl space?
posted by tomswift at 11:16 AM on April 10, 2011

I don't think the tank is the issue
Right, I was guessing this too. Now the question is indeed whether the pipes are copper or what else, or a combination.
I had a corrosion problem once at a point where copper went into a steel tank. Lead-to-copper would be just the same risk, in terms of potential corrosion.
Other than that, look especially at bends/corners on your drawings. Pipes expand and contract (even cold-water pipes), so angles get stressed more than straight sections (unless some part of the concrete has set sideways, obviously). Good luck.
posted by Namlit at 11:18 AM on April 10, 2011

have you tried turning off each shutoff valve on the other end of the line, i.e. the toilet, sink, icemaker, ect? At least you can determine if the leak is in an appliance or the floor.

Another good suggestion, I'll try this. However, my guess is I would see the leak if it was after the shutoff on an appliance. Worth a try though.

where are you..?. if you're in a cold climate, it's very unlikely the plumbing is in the "slab"... You're sure there's no crawl space?

In Colorado, so yes a cold climate. I am sure there is no crawlspace.
posted by cosmac at 11:32 AM on April 10, 2011

Is the valve for the house upstream or down stream of your pressure valve. If it is upstream it is probably the foot valve on your well pump system leaking water back into the well.
posted by Mitheral at 11:40 AM on April 10, 2011

I shut the valve that comes in to the house from the well that feeds the pressure tank (and the house). Still see a pressure drop. There is another valve after the pressure tank that feeds the house cold water. If I shut that the pressure holds. So I am pretty sure it is the cold water pipes in the house somewhere.
posted by cosmac at 11:55 AM on April 10, 2011

I think you have a leaking toilet tank flapper. These can be very insidious. You should close the valve(s) to any toilets and check again. If this is the problem, look in the toilet bowl and see if there is a slight cascade of water down from the rim. The side of the bowl will be wet even if the toilet hasn't been flushed for hours. Clean and/or replace the flapper valve. Well water can have a small amount of grit that deposits on the tank outlet under the flapper. This is just enough to cause a minor, minor leak.
posted by Old Geezer at 12:40 PM on April 10, 2011 [1 favorite]

The classic test for a leaking flap valve is to add some dye to the water in the toilet tank. Wait a while, and if you can see any dye in the bowl then the valve is leaking.
posted by Daddio at 12:49 PM on April 10, 2011 [1 favorite]

I've turned off all shutoff valves to all sinks, toilets, washer. Still losing water pressure. Starting to lose hope it is something simple (cheap).
posted by cosmac at 12:55 PM on April 10, 2011

Any outside faucets that might have suffered damage during an early cold snap at some point?
posted by HLD at 1:14 PM on April 10, 2011

If the pressure drop really disappears when you close the (cold) water supply valve to
the house, between the pressure tank and the house, you have a leak somewhere
in your piping downstream of the valve.

If it's not leaking inside the house, and it's not leaking through the appliances to a
drain (like toilet or washing machine or dishwasher, etc), then it's leaking in the slab,
assuming that your pipes are embedded in the slab.

Leaks in slabs can be detected thermally, if they're hot water (the slab warms up a
little where the hot water leak is), and probably even if the water is cold (the slab will
be colder where the leak is). 5 psi a minute is a pretty big leak. You might be able to
detect the leak location yourself with an infrared non-contact thermometer, which is
about 50 bucks on amazon. Radiant heating will interact with your heat based detection
process (maybe making a cold water leak easier to detect).

Intuit or infer the pipe runs in your slab, and start checking along their lengths with
the infrared unit.

Alternately, there are services that use an ultrasonic leak detector to find these leaks in
slabs. They'll pinpoint it close enough so that you just destroy a 1x1 foot piece of floor,
carefully, to install a patch. It's a thousand or two to get the leak detected (a few years
ago), but that's just the beginning :-) Homeowners insurance might help.
posted by the Real Dan at 1:15 PM on April 10, 2011

I've looked at all the external faucets, no sign that I can see of leaking from them or in the wall. It is a cold water leak, I've shut the valve that feeds the hot water tank and that doesn't help. No radiant heating in the slab (I wish!)

Interesting info on the leak detection technologies, Real Dan. I may contact one of these companies first and see what they say. I'll also contact the insurance company just in case.

Thanks for all the suggestions.
posted by cosmac at 2:08 PM on April 10, 2011

What covers the slab? If it is a concrete slab covered with something like carpet, I would guess you might be able to pinpoint a leak of this size using just a standard moisture meter.

Chances are that most of the moisture is not going into the carpet, but I have to imagine that the carpet above the leak will have more moisture than the surround (think 16% instead of 10%).

I don't mean wet to the touch, but a simple conductivity based moisture meter can probably detect the can get one for probably around $40.

A wood floor over the slab might show a similar difference in moisture content...
posted by NoDef at 5:48 PM on April 10, 2011

I hired a leak specialist and we've isolated it to the baseboard hot water system (I thought I had shut it off but got the wrong valve). So I do have a leak under the slab, somewhere. I will need to add valves and taps to each of the zones so we an isolate the boiler and use high pressure water or helium to pinpoint the leak. Not doing anything until I come to some agreement (or not) with the insurance company...
posted by cosmac at 10:33 AM on April 19, 2011 [1 favorite]

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