A slab foundation is a strong, flat layer of concrete that serves as the base and floor of a building. Concrete is durable, but a cracking foundation, water intrusion, poor construction, and aging can cause slab leaks over time. 

If your home has a concrete slab foundation, early slab leak detection is crucial to avoid severe structural damage, expensive repairs, and reduced property value. In this guide, we’ll cover some of the most common signs of a slab leak.

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Foundation Crack Repair

Foundation crack repair costs between $250 and $800.

Side of house with serious foundation damage.
Foundation Leak Repair

Depending on severity, leak repair can range from $2,000–$7,000.

Sinking concrete foundation in need of mudjacking leveling repai
Sinking Foundation Repair

The average cost for sinking foundation repair ranges from $500–$3,000.


What Is a Slab Leak?

A slab leak is when the plumbing pipes beneath a home’s concrete slab foundation—mainly copper water lines—corrode or otherwise deteriorate and leak water. If you suspect a slab leak, you need to investigate and address the issue right away, as it can cause damage to your home if left unresolved.

Causes of Slab Leaks

Understanding the following common causes of slab leaks can help you take preventive measures and address potential issues before they escalate.

  • Abrasion: Water or debris flowing through the pipes can erode pipes and cause leaks.
  • General corrosion: As pipes age, chemical reactions can cause them to corrode, weaken, and eventually leak.
  • High water pressure: High pressure can stress and weaken pipes.
  • Improper installation: A poorly installed plumbing system may have loose connections beneath a slab.
  • Shifting foundation: Soil movement or seismic activity can damage pipes beneath a slab.
  • Water acidity: Acidity caused by rainwater, soil, pollution, or decaying organic matter can corrode pipes and create leaks.

Signs of a Slab Leak

There are several signs that plumbing problems are lurking beneath a slab, including high water bills, wet spots on the floor, cracks in the walls, and unexplained mold or mildew growth. Watch for the following warning signs to avoid severe consequences of concrete slab leaks.

Cracks in Walls or Baseboards

As moisture from a slab leak penetrates the floor from below, it can cause visible cracks on the lower sections of interior walls or baseboards. These cracks can vary in size, though they often start as minor hairline fractures that widen over time.

A structural issue can also lead to wall cracks, so you should always hire a professional to evaluate them.

Hot Spot Areas on Your Floor

Imagine walking through your home barefoot and feeling warm or heated areas in random spots on the hardwood floor above your foundation. Known as hot spots, these localized sections typically align with the path of a leaking hot water pipe.

Not only do you need to be concerned about a leaking hot water line, but prolonged exposure to hot spots can be dangerous for young children and pets and may cause skin irritation or burns.

Low Water Pressure

If you can’t rinse the shampoo out of your hair in the shower or your dishwasher takes a long time to fill with water, you may have low water pressure.

Water escaping from a broken pipe beneath your slab can reduce water pressure throughout your home’s plumbing systems. The same can happen with clogged or damaged pipes, making it difficult to complete daily tasks.

Sounds of Running Water

If you hear the sound of running water, but the shower, sink faucets, dishwasher, and washing machine aren’t running, there could be a leak under your slab. The sound may be intermittent or continuous, but its persistence will likely give it away. 

Listen carefully to find the source, as a leak can be anywhere there are pipes, including behind drywall. Watch your water meter, too, to see if it continues to show water usage despite having all your water sources turned off.

Standing Water Around Your Home

If you have a slab leak, you may observe water pooling outside your home near the foundation or exterior walls. Standing water in basements or puddles in garages are other common signs.

While standing water is a concern, excessive rainfall can also create pooling. To differentiate between rainwater and a potential slab leak, look for standing water that remains for days after dry weather.

Sudden Increase in Your Water Bill

The average monthly water bill in the United States for a family of four is $72.93. Your average bill may be higher or lower based on your location and water usage, but make note of your average monthly total. 

While you can expect your bill to go up when enjoying summertime activities such as gardening or cooling off in the sprinkler, a significant or unexpected increase is worth investigating. Even small leaks in your home, including beneath your slab, can waste as much as 90 gallons of water per day, according to the U.S. Environmental Protection Agency (EPA).

Unpleasant Mold or Mildew Smell

Smells related to cooking and pets can pop up in a home, though they fade with time. A musty or earthy smell can signal the presence of mold or mildew—a dangerous side effect of slab leaks.

Unlike temporary odors, the smell of mold or mildew is persistent and can become distinct and unpleasant. Since mold and mildew can pose health risks, reach out to a professional right away if you notice this smell and suspect a slab leak.

Wet or Damp Carpets

If areas of your carpet feel damp or wet to the touch, even when there hasn’t been a recent spill, you may have a slab leak. These moist patches are often found near walls or baseboards since the water seeps upward into the carpet from underneath.

One-time spills or pet accidents dry and don’t return. A persistent dampness that reappears despite drying can indicate an ongoing issue.

Our Conclusion

Knowing the common signs of slab leaks, including low water pressure, cracks in the walls, and unexplained high water usage, is crucial to safeguarding your home’s foundation. Taking proactive measures, such as routine inspections and plumbing maintenance, can protect your finances and peace of mind. 

Contact a professional plumber immediately if you suspect a slab leak or notice any concerning signs. Early detection can help minimize the cost of repairing a slab leak.

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FAQ About Signs of a Slab Leak

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