How to Find, Diagnose, and Repair a Slab Leak (Signs, Temporary Fixes, and When to Call a Pro)

What is a slab leak?

A slab leak is water escaping from a pressurized water pipe located within or under the concrete slab foundation of a home (under slab-on-grade or within the slab itself). ^[1]

Common signs of a slab leak

• Unexpected increase in your water bill with no visible above-grade leaks; a water-meter test is a recommended first check. ^[1][5]
• Warm spots or a warm line across finished floors when a hot-water line under the slab is leaking; thermal imaging often reveals these. ^[1]
• Damp or soft floor areas, unexplained flooring discoloration, mildew or musty odors, or localized mold near the slab. ^[1][2]
• Low water pressure, hissing or running-water sounds when fixtures are off, or sporadic loss of hot water. ^[2][1]
• Exterior indicators such as sinkholes, wet patches in the yard near the slab, or soil movement/settling around the foundation. ^[2][1]

Immediate homeowner actions

The single best immediate step is to shut off the water main to stop flow and limit damage, then contact a plumber. ^[2][1]

DIY diagnostic steps you can do now

1. Water-meter test. Shut off all water inside and outside, record the meter or leak-dial reading, wait (typically 15–60+ minutes) without using water; any movement indicates a leak on the house side. This is a simple recommended first check. ^[5][1]
2. Isolate hot vs. cold. Turn off the water heater and re-test or listen; if the meter stops moving the leak is on the hot side. ^[2][5]
3. Listening/trace. Professionals use electronic acoustic listening devices to follow escaping water; homeowners may sometimes hear running water or notice warm lines on the floor surface. ^[1][2]

Professional diagnostic tools and what they do

Before removing concrete, professionals commonly use a mix of tools to localize a slab leak:

• Electronic acoustic detectors and correlators to pinpoint sound of escaping water. ^[1]
• Infrared thermal imaging, which is effective at locating warm-water leaks under tile or concrete. ^[1]
• Tracer gas (where permitted), pressure and dye tests, moisture meters and surface probes, and exploratory coring as needed. Moisture meters and surface probes can detect elevated moisture under flooring but are not precise for depth. ^[1][2]

Repair options — pros and tradeoffs

Common repair approaches include:

• Break & repair (open slab). Cut the concrete, repair or replace the failing pipe, then patch the slab and finishes. This is direct and permanent for accessible spots, but it is disruptive and costly because of demolition and finish repairs. ^[2][1]
• Reroute piping outside the slab. Run new supply lines through walls, the attic, or exterior paths to avoid slab demolition. This avoids cutting concrete but can create visible runs and require finish repairs elsewhere. ^[2][1]
• Trenchless / pipe relining. Epoxy lining or cured-in-place liners can be minimally invasive in some situations, but applicability for pressurized potable supply lines under slabs depends on pipe material, diameter, failure type, and the provider's claims. ^[2][1]
• Full repipe. Replacing all old lines is recommended for widespread corrosion or systemic failures; it is a long-term solution but typically the most costly and may require extensive access work. ^[2][1]

Temporary homeowner fixes — what they do and don't do

For accessible above-grade leaks, two-part epoxy putty (manufacturer example: Oatey Fix-It Stick) or self-fusing silicone tape can provide short-term emergency sealing. These are temporary emergency fixes and are not permanent repairs. They are not appropriate for under-slab leaks and do not address the underlying problem of a slab leak. ^[8][2][1]

Causes and materials notes

Copper pinhole leaks under slabs are often the result of internal corrosion (pitting) influenced by water chemistry and burial conditions; this is a documented mechanism for slab leaks in copper piping. ^[9]

Installation guidance for PEX under slabs recommends proper bedding, placement relative to reinforcement, and other practices to reduce abrasion and future damage risk. Follow manufacturer and industry installation guidance when installing or replacing in-slab piping. ^[7]

Safety, permits, and code considerations

Cutting or coring concrete releases respirable crystalline silica. OSHA’s construction silica standard (29 CFR 1926.1153) requires dust controls (for example, wet cutting) and appropriate respiratory protection when sawing or coring concrete. ^[6]

Model plumbing codes such as the International Plumbing Code include sleeve, clearance and penetration requirements for pipes passing through slabs and walls. Check local adopted codes and permits before making slab penetrations or repairs. ^[10]

Costs and hiring a pro

Consumer and industry sources report differing cost ranges for slab leak detection and repair; available guides and services disagree on exact typical figures. Consult multiple estimates and ask any contractor for an itemized scope before work begins. ^[3][4][2][1]

When to call a professional

• If the water-meter test shows continuous flow with all fixtures off. ^[5]
• If you suspect an under-slab leak from warm floors, moisture under finishes, or exterior yard wet spots. ^[1]
• If you hear running water inside walls or slab areas, have low pressure, or see signs of structural soil movement. ^[2][1]

Further reading and sources

Sources for the facts in this article include industry and trade guidance, plumbing services, and safety/code documents. See referenced sources in the footnotes above. ^[1][2][5]