What is a Slab Leak?

Last Updated On November 30, 2021
what is a slab leak

Have you been told you might have a slab leak? What exactly is a slab leak, how do you confirm you have one, and what repair options exist?

In this PlumbingNav guide, we will cover:

  • What is a slab leak? 
  • Signs to identify a slab leak
  • Supplies you’ll need to confirm a slab leak
  • What to do if I have a slab leak

What's In This Guide?

      What Is A Slab Leak?

      Every home is built on a foundation. In some parts of the country, your home sits directly on a concrete slab. Because plumbing supply and drain pipes are placed before the cement for the slab is poured, any future leak that develops in a supply line occurs “under the slab.” So, a water leak that originates from a pipe located under your concrete slab is a slab leak.

      Slab leaks range from being as small as a pinhole, to longer cracks that run horizontally through the pipe. When left undetected, a slab water leak can generate 10,000 gallons of wasted water per household or 1 trillion nationwide! 

      It’s more common for supply lines to be responsible for slab leaks, however, leaking drain pipes are also behind slab leaks as well.

      What Causes Slab Leaks?

      All types of pipes can develop a leak. Metal pipes such as copper do resist corrosion but are not corrosion-proof. Plastic pipes, including Pex, can also develop a water leak. How?

      Here are some common causes of slab leaks:

      • Manufacturing or Material Defects
      • Sediment / Wear
      • Excessive Water Pressure
      • Damage During Installation
      • Harsh Household Cleaners
      • Shifting/Settling of Concrete Placing Pressure or Torque on Pipes

      So how do you know if you have a slab leak? Gaining access to this part of your home can prove problematic. The easiest approach begins by looking for some common signs or symptoms of an under slab leak.

      How To Identify Signs Of A Slab Leak?

      How can you really tell what’s happening 2 to 3 feet underneath your concrete foundation to know if you have a slab leak? Look for the following clues to help identify a slab leak.

      Higher Water Bills

      Most homes have a relatively similar water bill from one month to the next, barring watering periods or hosting extended guests. When you notice that your water bill seems to be getting higher and higher with time, without much explanation, it may indicate a slab leak. 

      Low Water Pressure 

      Does your water not seem to have the same amount of pressure as it usually does, and you’re not running multiple water-consuming appliances? There is a reason, and this might be due to water “escaping” through an unseen leak.

      Most residential water systems have a pressure regulator set to 50 – 60 psi. If you’re on a well this will vary widely, but you will know if the pressure drops relative to what you normally experience.

      Water Spots On Floor

      The most noticeable indicator of a slab leak will be water spots on your floor that aren’t easily explained. Before you blame the dog or your child, finding a repeated wet spot on carpet or flooring in the same area might indicate a water leak beneath.

      If you experience wet spots on the floor it could be “finding a way out” from your concrete slab foundation and be originating from a slab leak below.

      Wet Spots on Exterior Foundation Walls

      Another sign of a slab leak can be isolated wet spots found on the outside of your home’s foundation. Obviously, a sprinkler or recent rain could be to blame. However, if you find this on one area of your foundation walls, it could be seeping out from inside. Leaking water builds up pressure, and it must escape.

      Supplies You’ll Need To Identify and Locate A Slab Leak

      Let’s talk about how you can confirm and locate a slab leak. We’ll talk about this from a DIY standpoint, and also when a professional plumber is necessary.

      First, let’s talk about how you can identify and test for a slab leak yourself. A DIY plumber is only as good as the tools available to them!

      These are some of the most common tools you’ll use to identify a slab leak.  


      An industrial plumbing endoscope feeds into your drain and provides you with an image of the inside of your drain thanks to a specialized camera on the end of the device. The flexible design allows it to maneuver through any plumbing system. 

      Electromagnetic Locator

      A locator at the source of the clog or leak can send signals to a receiver that allows you to identify exactly where the problem in your pipes is clearly. 

      In many cases, you can find locators automatically included in your endoscope. Some products will have a receiver included as well. If your item didn’t come with a receiver, you could use any receiver you may have for other power tools as long as they run on the same frequency.

      did you know what is a slab leak

      How To Identify A Slab Leak (5 Steps)

      Step 1: Shut Off Water

      First, you need to shut off the water to your home to prevent exacerbating the leak. 

      In most cases, you will find the main shut-off valve outside attached to the lower end of the wall or near your water meter. If you don’t know where to locate your water meter, look at your property paperwork or look for resources on your local government website. 

      Once you turn off the water at the main water line, you should open your faucets for about 30 – 60 seconds to allow any excess water to drain from the pipes. 

      Close all faucets before moving on to the next step. 

      Step 2: Check Water Meter

      Open the cover of your water meter using a screwdriver and read the meter to check for activity. 

      At this point, the reading should decrease until it gets to zero since you have the water off. You can tell that you have a leak when the water levels increase. 

      Step 3: Take Video Images of Inside Your Pipes

      At this time, it can help to get a visual of what’s happening in your pipes using an endoscope. 

      Feed your endoscope into your bathroom floor drain and watch your monitor as it goes deeper and deeper into your sewer line with your eyes open for signs of a clog or a leak. 

      Use a product specifically designed to help locate leaks as not all endoscopes can detect leaks. 

      A locator in the endoscope can help you pinpoint the exact location of the leak. 

      Step 4: Mark Location of Problem

      When you do notice an issue, you need to mark the exact location so that you can go back and resolve the problem at its source. 

      Since the leak probably developed under the concrete slab, it can be difficult to identify the exact location. However, record the data you have and locate the problem to the best of your ability. 

      Step 5: Clean Endoscope

      Once you finish getting your images, remove and clean the endoscope thoroughly. 

      Remember that the product is an electronic device with a camera that may not be waterproof, so be gentle when washing it with a damp washcloth.

      What To Do If You Have A Slab Leak?

      If you do have a slab leak, you will need to call a plumber with extensive experience regarding your home’s sewer line and other deep parts of your plumbing.  

      A number of factors will go into the final cost of your professional plumbing services. However, on average, you can expect to pay $400 if you have a plumber inspect for a slab leak.

      For foundation leak repair (including the inspection), you can expect to pay an average of $2280.

      Final Thoughts On What Is A Slab Leak

      A water leak can cause expensive water damage or mold. Slab leak detection can be difficult since it occurs underneath the foundation of your home. However, you can do it yourself with the right tools. 

      If you do run into multiple leaks that require plumbing repair, quick foundation repair can prevent future leaks and minimize the current damage. 

      FAQs For What Is A Slab Leak?

      How much do slab leaks cost to fix?

      It costs $2280 on average for slab leak repair. 

      What are the signs of a slab leak?

      Signs of a slab leak include:

      • High water bills
      • Low water bills
      • Moisture under your basement flooring
      • Rushing water sound

      How serious is a slab leak?

      You need to treat a slab leak seriously as it can lead to very expensive plumbing damage and water damage. 

      What exactly is a slab leak?

      In most cases, a slab leak refers to a damaged pipe underneath your concrete slab foundation.

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