DFW's expansive clay soil and post-tension slabs make this region a hotbed for slab leaks. Most start small — a pinhole in a copper line under the foundation — and quietly run for weeks before anyone notices. Here are the signs we look for, ordered by how reliably they indicate a slab leak.
1. Unexplained jump in your water bill
The most reliable early indicator. If your water bill spiked 30%+ with no change in usage, something is leaking. Not all of those are slab leaks, but a slab leak is the most common reason a leak runs undetected long enough to show up on a bill.
2. Sound of running water when nothing is on
Stand in the quietest room of the house at night. If you hear faint running water with all fixtures off, something is leaking somewhere — and if it's not a fixture, it's a pipe.
3. Warm spots on the floor
Hot-side slab leaks heat the concrete above them. Walk barefoot through the house in the morning before HVAC has equalized the floor temp. A localized warm spot is a strong tell.
4. Cracks in the slab or interior walls
DFW soil moves a lot anyway, but a sudden new crack — especially diagonal cracks above doorways — can mean water is undermining a section of the foundation.
5. Mildew or musty smell
Standing water trapped under the slab smells. If a corner of the house has gotten musty for no reason, check the floor for warm spots and check the closest wall for moisture.
6. Damp carpet or warped flooring
Late-stage symptom. By the time water is wicking up through the slab into your flooring, you've been leaking for weeks or months.
7. Dropping water pressure
A constant slab leak diverts water away from fixtures, especially during high-demand moments. If your shower pressure has crept down over months and other fixtures show the same, slab leak is on the list.
8. Water meter spinning with everything off
The definitive test:
- Shut every fixture off in the house
- Find your water meter (usually in the front yard)
- Watch the small "leak indicator" — a triangle, gear, or wheel
- If it's spinning, you have a leak somewhere
If the meter stops when you shut the main inside the house, the leak is on your side. If it keeps spinning, the leak is between the meter and the house — also a slab leak in many DFW homes.
9. Foundation hot to the touch (gas heaters)
Less common, but if you've ruled out water — natural gas slab leaks happen too. They're rare but dangerous. Smell of gas + a hot spot on the slab = leave the house and call the gas company immediately.
What to do if you suspect a slab leak
Step 1: Confirm there's a leak
Run the meter test above. If the meter is spinning, you have a leak. If it's not, you might be chasing a moisture problem instead.
Step 2: Isolate hot vs. cold
Shut the cold-water inlet to your water heater. Wait 30 minutes. Check the meter again:
- Still spinning? Cold-side leak.
- Stopped? Hot-side leak.
This narrows the search dramatically.
Step 3: Call a leak detection specialist
Don't open the slab on a guess. Electronic leak detection finds the exact spot before any concrete is cut, and the cost ($350–$650) is paid back many times over by not tearing up the wrong spot.
DFW slab leak repair options
You have three:
- Spot repair — open the slab, repair the section, patch. Cheapest. Usually $1,500–$3,500.
- Reroute — abandon the underslab line, run a new line through walls/attic. $2,500–$5,500. Often the right call for older copper.
- Whole-home repipe — if the whole system is failing, full PEX repipe. $6,000–$15,000.
For DFW homes built before 2000 with original copper under the slab, reroute is usually the smart play. We've seen too many "spot repaired" leaks come back as a different leak six months later.
Who to call
Sanchez Plumbing handles slab leak detection and repair across the DFW metroplex. Same-day diagnostic in most cases.
