Slab Leak Signs: How to Detect and What to Do

The most destructive leaks are the ones you can't see. Here's how to spot a slab leak before it becomes a disaster.

I'm Justin Sims, and of all the plumbing problems I deal with, slab leaks are among the most stressful for homeowners—and for good reason. When a pipe under your concrete foundation develops a leak, the damage can be extensive before you ever see a drop of water.

The key is catching it early. Let me show you what to look for.

What Is a Slab Leak?

Most homes in the Austin Hill Country are built on concrete slab foundations. The water supply lines and sometimes drain lines run through or under this slab, buried beneath inches of concrete and soil.

When one of these pipes develops a leak—from corrosion, shifting soil, or material failure—water seeps into the ground and potentially up into your home. Because the pipes are hidden, the leak can run for days, weeks, or even months before becoming obvious.

Why Slab Leaks Happen

Pipe Material and Age

Older homes (pre-1990s) may have copper supply lines under the slab. Copper can corrode over time, especially in contact with certain soil conditions common in Central Texas.

Galvanized steel pipes (even older homes) are also vulnerable to internal corrosion.

Polybutylene pipes (gray plastic, common in 1978-1995 construction) are notorious for failure and were the subject of class-action lawsuits.

Soil Movement

Texas clay soil expands when wet and contracts when dry. This constant movement puts stress on rigid pipes, leading to cracks and failures at joints.

Water Chemistry

Hard water and water with aggressive pH can accelerate pipe corrosion from the inside.

Poor Installation

Pipes that were kinked, inadequately protected, or poorly fitted during construction are more likely to fail.

Abrasion

Pipes can rub against concrete, rebar, or gravel over time. This slow abrasion eventually wears through the pipe wall.

The Warning Signs

1. Unexplained Spike in Water Bill

This is often the first sign. If your water usage jumps 25-50% or more without explanation, water is going somewhere—and it might be into the ground under your slab.

**What to do:** Check your water meter with all fixtures off. If the flow indicator is moving, you have a leak somewhere.

2. Sound of Running Water

If you hear water running when nothing is on—particularly a subtle hissing or whooshing sound—there may be pressurized water escaping under your floor.

**What to do:** Turn off all water sources and listen. The sound is often audible through the floor in the affected area.

3. Hot Spots on the Floor

If the leak is in a hot water line, you might notice a warm area on your floor—especially on tile or stone that would normally be cool.

**What to do:** Walk barefoot across hard floors and note any unusual warm spots. This can help pinpoint the leak location.

4. Wet or Damp Flooring

Persistent moisture, damp carpet, wet baseboards, or warped flooring near the foundation's edge can indicate water seeping up from below.

**What to do:** Investigate any unexplained moisture, especially along exterior walls or near plumbing fixtures.

5. Foundation Cracks

While some cracking is normal settling, new cracks or cracks that are actively growing could indicate foundation movement caused by soil erosion from a leak.

**What to do:** Monitor and document any cracks. If they're changing, consult a foundation specialist.

6. Mold or Mildew Smell

If water is pooling under your floor, mold can develop. You might smell a musty, earthy odor even if you don't see mold.

**What to do:** Don't ignore this smell. Mold is a health hazard and indicates ongoing moisture.

7. Low Water Pressure

If pressure has dropped throughout your home, a significant leak could be diverting water away from your fixtures.

**What to do:** Rule out other pressure issues (PRV, clogged filters) and consider slab leak if pressure drop is sudden.

8. Cracks in Walls or Ceiling

Shifting foundation from soil erosion can cause interior cracks, especially around door frames and windows.

**What to do:** Note whether these appeared suddenly or are growing.

9. Standing Water or Damp Spots in Yard

A slab leak that's severe enough might saturate soil to the point that it appears outside the home, usually near the foundation.

Confirming a Slab Leak

If you suspect a slab leak, professional diagnosis is essential. Here's what that looks like:

Pressure Testing

We isolate sections of your plumbing and pressurize them to identify which line is losing pressure.

Acoustic Detection

Specialized listening equipment can detect the sound of water escaping from a pipe, even through concrete. We literally listen for the leak.

Thermal Imaging

For hot water leaks, infrared cameras can visualize temperature differences, helping pinpoint the warm water pooling area.

Video Inspection

For drain line leaks, we can send a camera into the pipes to identify cracks, breaks, or root intrusion.

Helium Detection

In complex cases, we introduce helium into the line and use sensitive detection equipment to find where it escapes.

**Don't try to diagnose this yourself.** The precision required to minimize concrete demolition depends on accurate location—guessing is expensive.

What Happens If You Ignore It

Slab leaks don't get better on their own. Left unaddressed:

• **Water damage spreads:** Flooring, cabinets, drywall, and belongings can be ruined
• **Foundation damage:** Erosion under the slab can cause shifting, cracking, and structural issues
• **Mold growth:** Continuous moisture creates ideal conditions for mold, which is expensive to remediate and hazardous to health
• **Escalating costs:** A leak that could be fixed with spot repair might eventually require full repiping

Repair Options

Once we've located the leak, there are several repair approaches:

Spot Repair

For a single, accessible leak in an otherwise sound system, we can break through the concrete at that specific location, repair the pipe, and patch the concrete.

**Best for:** Newer homes with isolated failures

Pipe Rerouting

Instead of digging up the slab, we can abandon the damaged section and run a new line through the walls, ceiling, or exterior—bypassing the slab entirely.

**Best for:** Situations where slab access is difficult or the pipe condition is questionable

Full Repiping

If your under-slab pipes are old, corroded, or have failed in multiple places, replacing the entire system might be the most cost-effective long-term solution.

**Best for:** Older homes with widespread pipe deterioration, or homes with polybutylene pipes

Epoxy Pipe Lining

In some cases, pipes can be lined from the inside with epoxy coating, sealing small leaks and preventing future corrosion without excavation.

**Best for:** Specific conditions where traditional repair isn't ideal

Insurance Considerations

**The bad news:** Most homeowners insurance policies don't cover the actual pipe repair or detection.

**The good news:** Most policies DO cover the resulting damage—water damage to floors, walls, mold remediation, etc.

Key steps:

• Document everything before, during, and after repairs
• Get a professional assessment in writing
• File your claim promptly
• Keep all invoices

Check your specific policy, but don't assume you're not covered for the damage just because the repair itself isn't covered.

Prevention

Slab leaks are hard to prevent entirely, but you can reduce risk:

• **Monitor water bills** for unexplained increases
• **Install a water monitoring system** (Flo, Phyn, Flume) that alerts to unusual usage
• **Address soil drainage** to minimize expansion/contraction around foundation
• **Know your pipe materials** and their expected lifespan
• **Act quickly** if you notice any warning signs

The Bottom Line

Slab leaks are serious, but they're not the end of the world. Caught early and repaired properly, a slab leak is a fixable problem. The key is recognition—knowing the signs and acting quickly when you see them.

If you're experiencing any of the warning signs I've described, don't wait. The sooner we locate and repair a slab leak, the less damage and expense you'll face.