Pipes & water supply

Pipe leak under the slab foundation

A slab leak is a serious issue signaled by unexplained wet spots, warm patches on the floor, or a rising water bill, and requires professional leak detection rather than DIY digging.

Difficulty
Professional only
Time
1–3 days including detection and repair
DIY cost
N/A
Pro cost
$500–$4000+

Symptoms

  • Unexplained wet or damp spot on the floor with no visible source
  • A warm spot on the floor if it's a hot water line leaking
  • Sound of running water when everything is off
  • Mold smell or unexplained high water bill

Likely causes

  • CommonCorrosion of copper pipe running under the slabPipes in direct or near contact with concrete and soil can corrode faster than exposed pipe.
  • CommonGround shifting or settling stressing the pipeSoil movement over years can put pressure on rigid pipe, eventually causing a crack.
  • PossiblePoor original installation (pipe resting directly on rebar or rough concrete)Abrasion against a hard surface over years can wear through pipe from the outside.
  • Less commonWater chemistry accelerating corrosion from the insideAggressive water can attack the pipe from within even as it's stressed from outside.

What to do

  1. Turn off all fixtures and check your water meter for movement to confirm an active leak exists somewhere in the system.
  2. Note any warm spots on the floor (indicating a hot water line leak) or wet carpet/flooring in a specific area.
  3. Avoid trying to locate or dig into the slab yourself; specialized acoustic and thermal equipment is needed to pinpoint the exact leak location accurately.
  4. Call a plumber who specializes in slab leak detection, since guessing and cutting into the wrong spot can cause unnecessary damage.
  5. Once located, common repair options include rerouting the pipe above the slab, tunneling to access the specific leak point, or in some cases repiping the whole home to avoid future slab leaks.
  6. Check with your homeowner's insurance, since some policies cover a portion of slab leak repair costs.
  7. Address the leak promptly, since ongoing slab leaks can lead to foundation and mold problems beyond just the plumbing repair.

Tools and parts

  • None (professional detection required)

When to call a pro

Call a plumber specializing in slab leak detection immediately; this is not a DIY repair given the specialized equipment needed to locate the leak accurately.

Safety

Generally low risk

Generally low risk for a careful person. Stop if anything looks different from what this guide describes.

Related guides

Operator provides AI-generated troubleshooting information. It can be wrong. For safety-critical, electrical, gas, structural, medical, automotive safety, or other high-risk problems, consult a qualified professional.