Underground leak detection: the lines you cannot see

An underground leak is the one with no symptom. Indoors a leak eventually stains something. Outdoors, in this ground, it can run for weeks and leave the surface looking exactly as it always did — which is why the first sign is almost always the meter or the bill rather than a puddle.

Caliche: why nothing comes to the surface

Soils across greater Phoenix commonly hold clay, caliche or other hardpan at fairly shallow depth. Water leaving a buried pipe drops until it meets that layer and then does what water does: it runs sideways along the top of it. It follows the bedding sand in the trench it was laid in, or the gravel under a driveway, and it either surfaces somewhere unrelated to the break or it never surfaces at all.

Two practical consequences. First, the wet spot is evidence of where the water ended up, not of where the pipe failed — digging the wet spot is how a small repair becomes three holes. Second, the absence of a wet spot proves nothing. Plenty of the lines we locate had been losing water for weeks with a bone-dry yard above them.

What you notice instead

• The meter’s low-flow indicator turning with the house and the irrigation shut off.
• Pressure down at the far end of the property, or a hose bib that has lost its punch.
• A paver, a slab edge or a strip of driveway that has settled or cracked along a line.
• One patch of gravel that dries more slowly than everything around it.
• A bill that climbed and stayed up.

How a buried line is located

Prove the loss and isolate it

Shut the house at its main valve and watch the meter. Still moving means the loss is between the meter and that valve — buried. Stopped means it is inside. Shutting the irrigation separately splits the yard from the supply. Half an hour of valve work removes most of the property from the search.

Pressure decay

The isolated section goes on a gauge. A line that will not hold static pressure is leaking; how fast it falls says something about how big. This is the test that keeps us honest, because sound can be argued with and a gauge cannot.

Acoustic listening and correlation

Escaping water makes a continuous hiss that travels along the pipe further than it travels through soil. Ground microphones along the suspected route, and a correlator listening at two contact points, turn the loudest region into a mark on the ground. Background noise sets the floor here — pool pumps, air conditioning, traffic and wind all compete, so an early, quiet hour is genuinely better than a busy afternoon.

Line tracing

Before anything opens, the route gets mapped. Metallic pipe traces easily with a transmitter clipped to it. Plastic pipe with no tracer wire does not, so on those the route has to be worked out from the pressurised section, the entry and exit points and a sonde where one can be introduced. That is a real limitation and we say so on site rather than pretend the mark is more certain than it is.

What the method cannot do

Acoustics need pressure: an unpressurised line makes no noise to find. A slow weep in loose, sandy backfill can fall below what any microphone will separate from ambient noise. Concrete carries sound sideways, so a leak under a driveway can read loudest several feet from where it is. When the evidence does not agree, the answer is more isolation, not a bigger hole.

After the line is located

A single failure in otherwise sound pipe is a spot repair. A line that has failed more than once, or one running under finished hardscape, is often better replaced on a new route than chased under the old one — see leak repair, burst pipe repair and water main repair. We tell you which of those you are looking at before anything starts.

When it is something else

It is frequently irrigation rather than supply, which is why the irrigation valve gets shut first. It can be the pool plumbing under a deck, or the water main on the street side of the meter, which is usually the provider’s responsibility rather than yours. Sewer and gas lines are outside what we do at all.