The Ground Is Wet and Nobody Knows Why: Underground Water Leaks

A patch of lawn that never dries out. A dark line running across the berm when it has not rained for a week. A driveway that stays damp at one edge. Underground leaks announce themselves slowly, and by the time anyone rings us the water has usually been running for months.

The awkward part is that a wet patch is not proof of anything. Sometimes it is a split water main. Sometimes it is rain that has nowhere to go. Telling those two apart is the first job, and it is free.

Is it actually a leak, or just water in the ground?

Turn everything off inside and outside the house, then go and look at the meter. If the dial is moving with nothing running, water is escaping somewhere on your side. If it is completely still, the wet ground is not coming from your water supply.

We went to a property in Greenhithe where the ground was wet in several places and everyone assumed a leak. The meter was not moving at all. What was actually happening was rainwater running down the slope and pooling, with a suspect garden irrigation line as the only plumbing anywhere near it. The answer there was not a plumber chasing a leak, it was drainage.

That five minute check saves people a lot of money, which is why we tell everyone to do it before booking anything.

Where does my underground pipe even run?

From the meter box at the boundary, in a more or less straight line to where it enters the house. Underground water mains in New Zealand are blue, so if you dig anywhere on the property and find blue plastic pipe, that is your drinking water supply.

Older properties are the exception, and Auckland has plenty of them. You will still find galvanised steel, black polyethylene and copper in the ground, all of it well past the age where anyone would install it today. We repaired a split 20mm copper main under a house in Milford recently, and the honest advice afterwards was that the rest of that pipe is exactly the same age as the bit that failed.

Whose pipe is it, mine or Watercare’s?

The dividing line is the point of supply, which in practice means the meter. Watercare owns the connection and the meter. Everything from there to your house is yours to maintain and yours to fix.

So a wet patch between the street and the meter is a phone call to Watercare on 09 442 2222 and costs you nothing. A wet patch between the meter and the house is yours. If you cannot tell which side it is on, shut your water off at the meter: if the meter keeps turning, the water is escaping before it reaches your valve, and that is Watercare’s.

Why can you not just find it with a listening device?

Sometimes we can. Acoustic leak detection works by listening for the hiss of pressurised water escaping, and on a shallow pipe in the right ground it will put a mark within a metre.

It is not magic, though, and we would rather say so up front. On a job in Remuera the owners had high water usage and no visible leak anywhere. A leak detection company attended and could not pinpoint it, because the pipe was buried deep and the soil type absorbed the sound. We cut the concrete at the meter and capped off the line running to the pool to rule it out, and the meter kept running, which told us the leak was still on the main run. The detection company came back a second time and marked a spot at the rear of the property. We excavated exactly where they marked, and there was nothing there.

That is the reality of deep pipe in absorbent ground. Anyone who promises to find every leak first time is selling something.

So do you repair it or replace the whole thing?

This is the decision that actually matters, and it comes down to arithmetic rather than plumbing.

Chasing a leak on an old buried pipe means paying for detection, paying for excavation, making good the ground or the concrete afterwards, and accepting that the same pipe can fail again a metre further along next winter. At some point the cost of chasing exceeds the cost of simply putting in a new run, and on that Remuera job that is where it ended: a new water main.

When the pipe is modern, the leak is shallow and the location is confirmed, a repair is the sensible answer. When it is old galvanised or deep and nobody can pinpoint it, replacing the run is usually cheaper than finding it. We will tell you which one we think you are looking at before you spend anything.

What is involved in a new water main?

Less disruption than people expect, because the new line does not have to follow the old one. On a job in Glenfield we ran a new 25mm main from the meter box along the fence line and round to the rear of the house and garage, with brass elbows at the corners, UV tape at the fittings and the exposed section sleeved in PVC so the sun cannot get at it. A pressure limiting valve went in at the start of the new line while everything was open.

That last detail matters. If you are replacing the main anyway, fitting a limiting valve at the same time protects every hose, tap and fitting in the house from then on, and it costs very little while the trench is already there.

If your meter is turning and you cannot see why, call us. We will tell you honestly whether it is worth chasing or worth replacing.

Common questions

How much water can an underground leak waste before anyone notices?

A great deal, because there is nothing to see. Water escaping underground soaks away, and the only symptoms are a slightly damp patch and a water bill that has quietly climbed. We regularly find leaks that have been running for months. This is why the meter check is worth doing once a season even when nothing looks wrong.

Can I claim the extra water on my bill?

Watercare has a leak allowance process for exactly this situation, where a hidden leak has been found and repaired. You generally need evidence of the repair, which is where our invoice and report come in. It is worth asking, because on a long running underground leak the water charge can be larger than the repair.

Will you have to dig up my driveway?

Not necessarily. A new main can usually be routed around hard surfaces, along a fence line or through a garden, rather than back through concrete. Where a driveway genuinely has to be crossed, that is a cost worth knowing about before work starts, and we will say so in the quote rather than discovering it on the day.

How long will I be without water?

For a straightforward repair, a few hours. For a new main, we normally keep the existing line live while the new one goes in and only switch over at the end, so the actual outage is short. If you have particular timing needs, tell us before the day and we will plan the changeover around them.

The ground is wet but the meter is still. What now?

Then it is not your water supply, and the usual answers are surface water, groundwater, a broken stormwater or waste line, or an irrigation line downstream of a garden tap. Dirty water or a smell points at waste. Clean water that only appears after rain points at drainage, and the fix there is subsoil drainage rather than plumbing.