How We Actually Find a Hidden Leak, and What Each Stage Costs You

People imagine leak detection as a device that goes beep over the right spot. Some of it is that. Most of it is elimination, done in an order, and the order is what keeps you from paying to open the wrong wall.

This is what actually happens, what each stage can and cannot tell you, and why the investigation gets charged even though it has not fixed anything yet.

Stage one: prove there is a leak

Free, and you can do it before we arrive. Turn everything off and watch the meter.

A moving meter proves water is escaping from the pressurised side. A still meter does not prove the opposite: a slow concealed weep may not register at all, which is why a ceiling can be wet with a meter that has not moved. The one minute check is how to do it properly, and knowing the rate before we arrive genuinely shortens the visit.

Stage two: divide and re-test

This is the part that does the real work, and it is unglamorous.

We shut things off in sections and watch the meter again after each one. Isolate the cylinder: does it stop? Isolate a bathroom, the outside taps, the irrigation. Each answer removes a chunk of the house from suspicion.

A house often has more than one leak at the same time, so a repair has to be re-tested rather than assumed.

At a rental in West Harbour the meter was running with no water in use. Both toilets were leaking. We isolated the supplies to both and checked the meter again, and it was still running, so there was a concealed leak in addition to the two faults we could already see.

This is why we re-test after every repair. Fixing something we found means that fault is dealt with; it does not by itself mean the property is now watertight. If nobody checks, the toilets get repaired, the next bill is still high, and the owner reasonably wonders what they paid for.

We would rather tell you at the start that a repair may not be the end of it. Where we finish a job and the meter has gone still, we can say the property is clear. Where the meter is still moving, we say that too, and we keep going.

Stage three: narrow it physically

Once a zone is identified, the tools come out. Each does one job.

Pressure testing a section tells you whether that section holds. It proves a length of pipe is sound or not, which is often more useful than trying to hear the leak.
Moisture meters and thermal imaging read what is behind a surface without opening it. They find wet framing and warm lines. They do not see pipes, and they are read alongside everything else rather than trusted on their own.
Acoustic detection listens for the hiss of escaping water. On a shallow pipe in the right ground it will put a mark within a metre.
CCTV is for drains rather than pressurised pipe, and it answers a different question: not where is the water going, but what is in the line and where.

What detection cannot do

We would rather say this up front than have you discover it at your own expense.

Sound is the basis of most leak location, and depth, soil type and concrete all absorb it. On a job in Remuera the owners had high usage and nothing visible. A detection company attended and could not pinpoint it, because the pipe was buried deep and the soil absorbed the sound. We cut the concrete at the meter and capped the line to the pool to rule it out, and the meter kept running. The detection company returned and marked a spot at the rear of the property. We excavated exactly where they marked, and there was nothing there.

Sometimes it works first go. In Henderson, detection pinned a burst under the concrete near an outdoor hose tap, we cut one hole, replaced the section and reinstated it. Shallow pipe, sensible starting hypothesis, clean result.

Both of those are normal. Anyone who guarantees to find every leak first time is selling something.

Stage four: open something, carefully

When it is inside a wall or ceiling there is eventually no substitute for looking.

We do it as late and as little as we can. On a Takapuna job the meter was not moving at all, so we moisture tested the walls and checked the fixtures above, then recommended opening the linings and got approval before doing it. On the second visit we opened the ceiling and wall progressively, tracing as we went rather than removing a whole sheet, and found a slow leak at a corroded tee inside the wall.

One careful hole in the right place beats three in the wrong ones.

Ceiling and wall linings opened progressively to trace a concealed leak

When to stop looking and replace instead

This is the decision that saves the most money, and it is an arithmetic question rather than a plumbing one.

Every further attempt to locate costs money, and on an old buried pipe the same line can fail again a metre away next winter. At the point where detection attempts plus excavation plus making good exceed the cost of simply running a new line, stop looking.

That West Harbour job ended there: once the underground main between the meter and the house was confirmed as leaking but not pinpointed, the recommendation was to replace roughly 15 to 20 metres of it with new pipe rather than keep hunting. The Remuera job ended the same way, with a new main.

The new pipe does not have to follow the old route, so it can avoid the concrete entirely. More on that decision here.

So what am I paying for?

Three separate things, and it is fair to ask which one you are being quoted for.

Investigation. Confirming, isolating, testing and locating.
Repair. Once the fault is exposed, this is usually the smallest part of the bill.
Making good. Concrete, gib, paint, landscaping. On a lined wall or ceiling this is a builder’s quote, not ours.

The best outcome is that we find it quickly and the whole thing happens in one visit, and plenty of jobs go that way. But a leak is hidden by definition, and hidden things can take more than one look. It is fair to expect that some jobs need a second or third visit before the water is actually stopped, and it is better to know that at the start than to find out on the day.

For the same reason we quote the stages as they become knowable rather than pretending to know the total on day one. If someone gives you a single fixed price to fix a leak nobody has located yet, ask them how.

Meter moving and no idea why? Call us with the rate you measured off the meter. It tells us more than a description does.

Common questions

Can you find it without opening or digging anything?

Often, yes. A great many leaks are located by isolation and testing alone, without a single hole, because narrowing it to one line and pressure testing that line answers the question. Where it fails is deep buried pipe and leaks concealed inside linings, and those are the jobs where the honest answer up front is that some opening is likely.

Why did the detection company not find it?

Usually depth and ground conditions rather than anything they did wrong. Acoustic location needs the sound to reach the surface, and dense or absorbent soil, deep pipe and a slab all work against that. It is also possible for a mark to be slightly off and an excavation to miss by half a metre. This is a real limitation of the method, not a sign of a bad operator.

Is thermal imaging worth paying for?

It earns its place on hot water leaks and on wet building materials, where a temperature difference actually exists to see. It does not see through walls and it does not find cold water leaks that have not wet anything yet. Treat it as one input among several rather than the answer on its own.

How long does the whole process take?

A leak that isolation finds can be located and repaired in a single visit. A concealed one is commonly two or three: investigate, get approval for the next step, then repair, sometimes with a specialist visit in between. Where we can, we make the property safe on the first visit even if the full repair has to wait, because stopping the water is usually more urgent than finishing the job.

Do you check for other leaks while you are there?

Yes, and we check the meter at the end of every job whatever we came for. That is how we found an under-concrete leak at a Sunnynook property while we were there to fix a toilet. It costs us a minute and it has saved owners a great deal.