Slab Leak Detection and Repair
A slab leak is a supply line failure under the foundation, and it runs continuously because the water has nowhere visible to go. Warm spots on the floor, an unexplained water bill spike, and the sound of running water with everything off are the classic signs. Detection plus repair typically runs $1,200 to $4,500.
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How urgent is this? Urgent but rarely a middle-of-the-night call. The damage is continuous and worsens as soil erodes beneath the foundation, so it should be addressed within days rather than weeks, but detection work needs a quiet house and daylight anyway.
Typical cost: $1,200 to $4,500 nationally. Detection alone runs $350 to $800. A single accessible spot repair sits at the low end of the total. Post-tension slabs, which require cable scanning before any cutting, and multi-leak situations that justify a full repipe push toward and past the high end.
Warning signs
- A warm or hot spot on the floor, which indicates a hot water line leak
- Water bills rising sharply with no change in usage
- The sound of running water when every fixture is off
- Unexplained damp patches, buckling, or discoloration in flooring
- A drop in water pressure throughout the house
- Cracks appearing in flooring or walls as soil beneath the slab washes out
What causes it
- Abrasion where a pipe rubs against concrete or gravel as it expands and contracts
- Corrosion of copper lines from aggressive soil or water chemistry
- Foundation movement in expansive clay soils shearing rigid connections
- Poor initial installation, including inadequate sleeving where pipe passes through concrete
- High water pressure accelerating every one of the above
What to do before the plumber arrives
- Note exactly where the warm spot is, and when you first noticed it
- Take a water meter reading with everything off, wait an hour, and read it again; the difference documents the leak rate
- Gather recent water bills so the plumber can see when consumption changed
- Do not break into the slab yourself under any circumstances
- If the leak is severe, shut off the main between uses to limit ongoing damage
What the plumber will actually do
Confirm the leak exists
A pressure test isolates the supply system and confirms the loss is under the slab rather than elsewhere, which prevents a very expensive misdiagnosis.
Pinpoint the location
Acoustic listening equipment, thermal imaging, and sometimes tracer gas narrow the leak to within a small area. Precision here is the difference between one small hole in the concrete and several.
Choose the repair approach
The options are cutting through the slab to the leak, rerouting the line overhead or around the slab, or repiping the affected run entirely. Cost and disruption differ significantly.
Execute the repair
For a spot repair, concrete is cut, the pipe section is replaced, and the slab is patched. For a reroute, a new line is run and the old one abandoned in place.
Test and restore
The system is repressurized and verified, and the concrete and flooring are restored.
Slab leak repair FAQ
How do I know it is a slab leak and not something else?
The distinguishing signs are a warm spot on the floor with no heating source beneath it, a meter that keeps moving with every fixture closed, and a water bill that climbs without a change in habits. A pressure test confirms it. Do not authorize concrete cutting on symptoms alone.
Is rerouting better than repairing the leak in place?
It often is. A spot repair fixes one failure in a line that is the same age and condition throughout, so on an older copper system that has already leaked once, the next leak is usually a question of when. Rerouting abandons the under-slab run entirely and removes the whole failure category. It costs more up front and frequently less over ten years.
Does insurance cover slab leaks?
Policies commonly cover the resulting damage and the cost of accessing the pipe, meaning the concrete cutting, while excluding the pipe repair itself. Coverage varies considerably by carrier and state, and gradual-damage exclusions are frequently invoked. Read your policy language before assuming, and document when you first noticed symptoms.
Can a slab leak damage the foundation?
Yes, and this is the reason not to leave one running. Water escaping under a slab erodes the soil supporting it, and in expansive clay it also causes localized swelling. Either way the slab loses uniform support, which is how a plumbing problem turns into a structural one.
Related services
- Emergency Leak DetectionNon-invasive location of hidden water leaks behind walls, under floors, and beneath slabs using acoustic, thermal, and pressure testing equipment.
- Main Water Line RepairRepair and replacement of the buried water service line between the meter and the house, including trenchless replacement options.
- Emergency Burst Pipe RepairA burst pipe releases water continuously until the supply is shut off. Emergency repair covers isolation, pipe section replacement, and pressure testing.
- Whole-House RepipingReplacement of a home's supply piping where the existing system has reached end of life, using PEX or copper.
Emergency guides
Cost guides
- Slab Leak Repair CostWhat it costs to find and fix a leak under a concrete foundation, and when rerouting beats repairing in place.
- Water Heater Replacement CostWhat tank and tankless water heater replacement costs, including the code upgrades that appear on the invoice unexpectedly.
- Drain Cleaning CostWhat drain and sewer clearing costs by method and location, and when jetting is worth the premium over cabling.
Common questions
- Costs and Billing QuestionsHow emergency plumbing is priced, what the premiums are, and which questions to ask before dispatch.
- Water Heater QuestionsLeaks, no hot water, strange noises, safety valves, and the repair-or-replace decision.
- Drain and Sewer QuestionsBlocked drains, main line backups, recurring clogs, and what not to put down them.
Related articles
- What Emergency Plumbing Actually Costs, and WhyA plain breakdown of after-hours rates, call-out fees, and the four questions that change your invoice.
- Your Water Heater Is Telling You It Is About to FailTank heaters give several months of warning before they flood a floor. The signs, in the order they usually appear.
- If Your Basement Backs Up When It Rains, Your Pipes Are FineRain-correlated sewer backups are a municipal capacity problem, not a blockage. Clearing your line will not stop it.