How can I (or a plumber) locate a mysterious internal leak?

Question

Last week I got hit with a colossal water bill. After contacting the supplier I was told to conduct a stop tap test on my water meter. I was confident this would reveal an external leak as we'd seen no sign water is leaking anywhere indoors. However, the test indicate the leak is indeed internal.

The supplier said that we now need to get a plumber in - at our expense - to locate and fix the leak. But I find it hard to understand how on earth anyone can track down a leak when there's no evidence of any water escaping other than the meter showing.

The supplier suggested the likely culprits were toilets or the boiler. I don't really understand how a boiler can leak water without us knowing, so I checked the toilets and couldn't see any water escaping down the overflows. We don't hear water running anywhere although we do have a water softener which I suppose could be involved somehow.

What I'm really dreading is a plumber coming out and racking up a huge bill spending hours failing to find a leak. Is there anything I can do to try and locate this leak myself, and if not, what can a plumber do that I cannot?

Answer 1

General process would be to shut things off internally and repeat your stop valve test to see which thing or things affect the leak. How well you can narrow it down depends on how your plumbing is set up in terms of valves to shut off various supplies.

So, if you have an "inside the house main shut off," shut that. If the leak stops, it's past that point. If the leak continues, it's between the meter and that valve.

If the leak stops at the main shutoff, reopen the main shutoff. and bypass the water softener, and check the leak again.

Then, if you still haven't found it, shut off each toilet supply and recheck, etc.

If a boiler has a drain (for condensate, typically) that can take away water from a leak, depending where the leak is.

For toilets, some food coloring in the tank can show you a leak you may not hear - if the bowl turns color without you flushing, the toilet is leaking. Toilet leaks are more commonly not "down the overflow" but "around a poorly sealed flapper valve" - down the overflow is only when the fill valve is not shutting off as it should.

As commented, water softeners are a prime suspect, again, because there is a drain connection that takes away the "leak" so you don't get a puddle. Since those are normally installed with a bypass valve, or 3 valves you can use to bypass them in backwards states like Mass that don't allow a single, unscrew-up-able bypass valve, they are normally easy to check, via bypassing. After cleaning the valves in the one I had multiple times, and the problem recurring multiple times, it was an easy decision to replace the thing.

Answer 2

You don't say what country, but in the UK the pipe from the water company's stopcock to your premises is your responsibility. In older premises this pipe is quite probably iron, and can rust through.

That stopcock is usually in the public walkway outside your house, integrated with or adjacent to your water meter. Trouble is that you need a special key to operate it, that's not generally available to the public (lest anti-social types were to go around turning other people's water off!) Plumbers do have that key.

If this pipe is leaking it will be quite a major job to replace it with modern blue plastic water pipe between your internal stop-cock and the meter location. (Builders, a mini-digger, a complete mess of your lawn or flower-beds ...)

Answer 3

To answer your question generically, there are only so many places that water could be transferring from the supply lines to the drain lines. We can reasonably assume that this is what's happening since you have no visible evidence of leaks outside the drain system.

So make a list and investigate by listening and doing additional tap tests. You could also open a primary drain cleanout to help observe flow in various circumstances.

Some general suggestions:

• Sinks
• Toilets
• Tubs and showers
• Water softener
• Exterior water heater
• Radiative heating systems*
• In-floor heating systems*

* Should normally be closed-loops, but worth a check.

Answer 4

Hire a plumber with a leak detector

If you can’t find the leak and there is no obvious damage it’s likely the leak is underground. There are tools that “listen” for leaks and can pinpoint the leak within half a meter or so.

Answer 5

You're looking for a combination of a) a connection to utility water, and b) a place where that water could go without being observed. So right off the bat we can cross off spigots with sinks under them. You will see water moving from spigot to sink.

So next is toilets. Pop the lids off the tanks and see what's going on. There is never any moogie (human waste) in the tank, this is a fresh water supply. It's gross because it hasn't been cleaned in 20 years. Toilets have two places that can leak in stealth: the refill valve (attached to the float) and the flapper valve that dumps the big shot of water (attached to the handle). Start by observing the water level as compared to pipes in the bowl after the toilet has been quiescent (unused) for a half hour.

• There should be an open-top pipe risng at or above the top of the water. That is the tank overflow. Note the water level in its undisturbed state (long time since a flush). Go ahead and flush it and watch it refill. When the valve shuts off, you'll see the intended resting place of the water, and it should be about an inch below that overflow pipe. If over time it's climbing to the top of that pipe, that's refill valve leakage.
• If the refill valve is good, with the tank full block or tie the float in the "up" position so that it cannot fall down. Note tank water level and leave it that way for 10 minutes. Has tank level fallen with the float up? That is a flapper valve leak.

Next, look at your water heater. It should have an over-pressure valve to a pipe. Often these dump on the floor or into a tray under the water heater. If they are fully plumbed to dump outdoors, follow the pipe to its outlet and see if water is dribbling or flowing there.

Next, a leaky water softener valve is a possible culprit. However, water softeners have a special drain for purge water. It isn't dumping water into the supply piping! Follow that plumbing and look at flow there.

Next, if you have a hydronic furnace, it may have the capacity to refill itself from supply. It will also have an overpressure valve- same deal as the water heater. Hunt it down and follow the piping to the outlet.

We can cross off an internal pipe leak within your home. Tens of thousands of gallons leaked that way would cause heinous mold and mildew problems.

Also check outdoor taps for being broken, especially if the valve is kept on 24x7 with a hose attached.

Lastly look for wetter-than-normal parts of the yard, or an extra-green or extra-tall patch. If you lived in the southwest this would be immediately apparent by the grass not being brown. If you have green grass because you have irrigation, shut that off! Both to test if the leak stops when you do, and also to distress your lawn - if some part of the yard does not start turning brown, that reveals the leak.