Guide · Updated Nov 5, 2026
Slab leak detection: how pros find under-slab leaks and what it costs
You hear water running with every tap off. The bill climbed for no reason. A warm spot showed up on the tile. Slab leak detection is how pros locate the break under the concrete before anyone starts breaking or tunneling. In San Antonio clay, finding the leak is step one; checking the foundation afterward is step two.
Picture this
Here's a typical scenario (not a real customer). A homeowner ignores a slow bill increase for a season. Detection finally finds a pinhole under the hallway. The plumber fixes the pipe. Months later a door starts to rub because the wet soil under one bay of the slab never matched the drier soil next to it. Detection fixed the plumbing mystery; nobody scheduled the foundation check.
How pros find under-slab leaks
- Pressure and meter checks. Confirm water is leaving the system when fixtures are off.
- Acoustic listening. Sensitive mics pick up the sound of water escaping under the slab.
- Electronic / correlating equipment. Helps narrow the location along a line.
- Infrared imaging. Warm or cool patterns on the floor can hint at water paths.
- Access when needed. Tunneling, small slab openings or reroutes come after the leak is located.
Ask the plumber which methods they will use and whether they will mark the location before cutting.
What slab leak detection costs (2026)
| Item | Typical 2026 range |
|---|---|
| Leak detection | ~$280 average ($150–$400) |
| Slab leak repair, national average (detection included) | $2,280 (most pay $630–$4,400) |
| Pinhole leak | $150–$800 |
| Reroute the line instead of breaking the slab | $600–$4,000 |
| Repairing the concrete slab afterward | $300–$6,750 |
| Permits | $150–$200 |
Source: Angi, How Much Does Slab Leak Repair Cost? (2026 data, updated Sep 22, 2026). National figures, not San Antonio quotes. Foundation repair, if needed, is separate. Full walkthrough: slab leak repair in San Antonio.
After detection: fix the pipe, then check the foundation
- Shut off water at the main if you see active damage.
- Hire a licensed plumber for detection and repair.
- Photograph cracks, gaps and damp areas with dates.
- Get a foundation inspection if you have movement symptoms or a long-running leak. See under-slab plumbing leak referrals.
- Call your insurer early; coverage varies. See insurance and foundation repair.
On Bexar County clay, uneven moisture can mean uneven movement (Texas Master Naturalist; TDLR).
Free foundation check after the leak
LevelSATX Foundation Network matches San Antonio homeowners with one vetted, independent network partner for a free foundation inspection after plumbing work, or when symptoms point to movement. We don't do plumbing or repairs. Partners pay us for referrals. Any company can apply to join the network.
Get my free foundation inspection match
Related: 7 signs you need foundation repair · slab foundation repair.
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Calculators and guides give ranges. A free inspection from one vetted, independent local contractor gives you a written quote. No cost, no obligation.
Get my free inspection →Frequently asked questions
How much does slab leak detection cost?
Angi's 2026 data puts leak detection alone at about $280 on average, typically $150 to $400. Full slab leak repair including detection averages $2,280 nationally, with most homeowners paying $630 to $4,400. These are national figures, not San Antonio quotes.
How do plumbers find a leak under a slab?
Common tools include acoustic listening, infrared cameras, pressure tests, electronic leak detection and, when needed, controlled access or camera inspection of lines. The exact mix depends on the home and the suspected line.
Should I get the foundation checked after a slab leak?
Yes if you see cracks, sticking doors, sloping floors, or if the leak soaked soil for a long time. Water under a slab can change soil moisture unevenly on San Antonio clay.
Who do I call first, a plumber or a foundation company?
Call a licensed plumber for detection and the pipe. A foundation company evaluates whether the slab moved and whether stabilizing work is needed. Many homeowners need both.
Is LevelSATX Foundation Network a plumbing company?
No. We are a free matching service for foundation inspections. Independent network partners evaluate foundations; plumbing repairs belong with a licensed plumber.
Keep reading
- Foundation repair cost in San Antonio: the 2026 guide
- Pier and beam vs slab foundation repair: cost, pros and cons
- 7 signs you need foundation repair in San Antonio
- Steel vs concrete piers: costs and trade-offs compared
- Foundation repair methods compared: what each costs and when it fits
- How to choose a foundation repair company in San Antonio: a checklist
- Slab leak repair in San Antonio: signs, 2026 costs and what to do first
- Best foundation repair in San Antonio: 10 criteria to verify
- Foundation repair warranty: what lifetime and transferable really mean
- How to compare foundation repair companies in San Antonio
- 12 foundation repair red flags in quotes, sales tactics and warranties
- Questions to ask a foundation repair company (with good answers)
- Pier and beam foundation repair: how it works and what it costs
- Foundation repair cost calculator
- House leveling and pier cost calculator
Sources cited on this page: Angi, How Much Does Foundation Repair Cost? (updated Oct 26, 2026); Angi, How Much Does Pier and Beam Foundation Repair Cost? (updated Sep 18, 2026); Angi, How Much Does Slab Leak Repair Cost? (2026 data, updated Sep 22, 2026); Texas Master Naturalist, Alamo Area Chapter: Bexar County Soils; Texas Dept. of Licensing & Regulation, Technical Bulletin IHB TB 10-01 (Foundations on Expansive Soils). Cost figures are national, not San Antonio quotes.
LevelSATX Foundation Network connects San Antonio homeowners with vetted, independent foundation repair contractors. We don't perform repairs; participating contractors pay us for referrals.