Slab leak detection in Phoenix homes

A slab leak is a pressurised water line failing underneath the concrete your house is standing on. Nobody sees it start. What people notice is one of a short list of small, strange things, and the gap between the first sign and the wet carpet can be months.

What it feels like before you see it

• One patch of tile or wood is warm underfoot and the rest is not — a hot-water line.
• A faint hiss or running sound with every tap in the house closed.
• The meter’s low-flow indicator creeping round with the house shut off.
• Hot water pressure down, or the water heater cycling more than it used to.
• Flooring lifting, grout darkening, or a baseboard staying damp in one place.
• A bill that climbed with nothing visibly wet anywhere.

Hot-water lines fail more often than cold ones, which is why the warm-floor symptom comes up so much — and it is also the symptom thermal imaging is genuinely good at.

Why this is a Phoenix problem

Slab-on-grade is the normal way to build here: the supply lines are run in or under the concrete rather than through a basement. Combine that with what is in the ground — clay, caliche and hardpan at shallow depth, and soil that moves through monsoon wetting and drying — and you have pipe that is both inaccessible and under stress.

Age decides the rest. The U.S. Census Bureau’s housing figures make the split across the Valley very clear: in Sun City about 88 percent of housing units were built before 1980, in the Encanto and Willo area about 75 percent, and in Arcadia about 67 percent, against a Valley full of 2000s subdivisions where the figure is in single digits. Copper of this era usually fails where it was bent or where it rubs a rebar chair, so the leak is rarely where the wet carpet is.

Source: U.S. Census Bureau, American Community Survey 5-year estimates (2023).

How it gets pinpointed

Prove it, then isolate it

First the meter, with everything shut. Then hot and cold are separated and tested independently, because knowing which system is losing pressure halves the search before any equipment comes out of the van.

Listen

A pressurised leak under concrete makes a steady noise that the slab carries. Ground microphones walked across the floor in a grid narrow it to a spot. Concrete and tile broadcast sound well, which is both why this works and why the loudest reading is not automatically the leak — see acoustic leak detection for what that equipment can and cannot hear.

Thermal, on the hot line

An infrared camera reads the surface. A hot-water leak warms the slab above it in a shape you can read through tile. On carpet and pad it reads much less, and on a cold-water leak in a house sitting at room temperature it may read nothing at all.

Trace the route

Knowing where the pipe actually runs matters as much as knowing where it leaks, because it turns one opening into the right opening.

What the equipment cannot tell you

It cannot see through the slab. Every method here is inference — pressure says a line is losing, sound and heat say roughly where, and the three are cross-checked until they agree. A very small leak at low flow can be too quiet to hear, in which case the honest answer is staged isolation rather than a guess. And a leak under a kitchen island or a cabinet run may be locatable to within a small area but not to the inch.

Post-tension slabs

Many Valley homes have post-tension slabs, with steel cables in tension running through the concrete. Those slabs must not be cut without proper assessment. That is precisely why the whole job is pinpointing rather than opening, and it is also why a reroute — abandoning the failed section and running new line above the slab — is often the better repair. See slab leak repair.

When it is not a slab leak

An air-conditioning condensate line, a shower pan, a toilet seal, a water softener discharge, a roof leak following a wall down, or an irrigation line soaking the soil against the footing. Those get ruled out before anyone talks about concrete. Fixtures and appliances themselves are outside what we do.