Slab Leak Warning Signs

By McKinney 24 Hour Plumber · Updated September 2026

A Leak You Hear Before You See

A slab leak is a failure in a water line running under or within the concrete foundation. Because the water has nowhere obvious to go, it can run for weeks without producing the puddle you would expect. Instead it shows up indirectly: a bill that climbs, a floor that feels wrong underfoot, a sound in a quiet house. That indirectness is what makes it worth knowing the signs, because the earlier it is found, the less soil is washed out from under the slab and the less flooring has to come up to fix it.

The Signs That Matter Most

A warm patch on the floor is the classic one, and it means a hot water line. Walk the house barefoot and you will find it if it is there. The sound of running water when every tap and appliance is off is another: stand still in a quiet room late at night and listen. Then there is damp that will not dry, carpet that stays cool and heavy in one area, wood flooring that cups or lifts, or grout and baseboards that stay discolored. A water bill that jumps with no change in how you use water belongs on the list, and so does hot water pressure that has quietly dropped on its own.

The Meter Test You Can Do Yourself

This one check is worth doing before you call anyone. Turn off every fixture and appliance that uses water, including ice makers and irrigation. Then open the meter box near the curb and look at the meter face. Most have a small triangular or star-shaped flow indicator that spins whenever water is moving. If it is turning with everything off, water is escaping somewhere on your side of the meter. That does not prove the leak is under the slab, but it does prove there is one, and it is the single most useful piece of information you can hand a plumber over the phone.

Why McKinney Sees So Many

Most of McKinney's post-1990 housing sits on a slab poured over Blackland Prairie clay, and that soil is unusually expansive. It swells when it rains and shrinks hard in a dry Texas summer, and it does that every year. The slab moves with it, and anything cast into or running beneath the concrete moves too. Add decades of hard water inside the pipe and you have a reasonable explanation for why slab leaks are a normal part of plumbing life here rather than an unusual event. Older houses closer to the downtown square are often pier-and-beam instead, with a crawl space underneath, which is a very different and usually easier situation. Newer growth areas such as Anna are almost entirely slab construction, so the same clay questions apply there even on young houses.

Things That Look Like a Slab Leak But Are Not

Plenty of problems mimic this. A leaking shower pan drips into the same general area. A failed wax seal under a toilet wets the floor around it. An irrigation line broken near the house soaks the ground outside and wicks in. A condensate line from the air handler can drip somewhere unhelpful. All of these are cheaper and easier to fix than opening concrete, which is exactly why a proper diagnosis isolates the system before anyone talks about a slab. If a company proposes breaking the floor before ruling those out, ask what testing was actually done.

What a Proper Diagnosis Looks Like

The sequence should be: confirm there is a leak, confirm which system it is on, then pinpoint the location. Pressure testing separates the hot side from the cold side and the supply from the fixtures. Listening equipment and moisture readings narrow it to a specific area of floor. Only then should anyone discuss opening the slab, and the opening should be small and in a defined place. You should also hear the alternatives: repairing in place through the concrete, rerouting the line overhead through the attic or walls, or replacing a whole run. Each has a different effect on your floors and your schedule.

Why Waiting Makes It Worse

A slab leak is not a drip you can live with. Water running continuously under the foundation washes out the soil supporting it, which worsens exactly the movement this clay already causes. It also raises humidity in the house and can damage flooring well beyond the leak point. On the hot side you are heating water that goes straight into the ground. The problem does not stabilize, so the only real question is whether it is dealt with now or later at greater cost.

Arrange an Inspection

If the meter is turning with everything off, call. McKinney 24 Hour Plumber explains what slab leak repair involves and how the line is located, and leak detection covers the testing that comes first. If the water turns out to be coming from the heater instead, our repair versus replacement guide covers that decision, or see how calling works.