A SLAB LEAK Is Caused By A Leaking Water-Supply Pipe — 17 Signs You Have One

slab leak due to cracked pipe

A Slab Leak Is Caused By A Leaking Water-Supply Pipe Under Your Home  

Your Water Pipes Are In The Soil Underneath Your Home’s Slab Foundation

The Term Slab Leak Is Commonly Heard In DFW,  It can be caused by either a leaking Water-Supply Pipe, or a leaking Sewer Pipe.  This article addresses only leaking Water-Supply pipes.  If you are seeking information on a Slab Leak caused by a leaking Sewer Pipe, read this article instead: Article About Slab Leak Due To Leaking Sewer Pipe.  Though the article’s Title is “Whole-House Sewer Clog” — leaking Sewer Pipes are covered in detail.

Most people think of a leaking Water-Supply Pipe (also called water line) when they say Slab Leak.  This type of slab leak is caused by a cracked or damaged Water-Supply Pipe.  As with most components within a home, Water-Supply Lines are subject to deterioration due to aging and can wear out or fail.  Often, though, Water-Supply Line Slab Leaks are caused by a cracked water pipe due to Slab Movement in DFW area homes (due to DFW’s expansive-clay soil).

Your DFW area home almost always has a concrete slab foundation upon which the house sits  During construction, the Water-Supply Pipes and Sewer Pipes are put into place in the ground where your home will sit.  After all underground components are installed, a plastic water-vapor barrier is laied (over the entire area where cement will be poured), the cement is poured and dries to a very strong concrete slab with supports the entire weight of the house.

photo of water pipes coming up from the ground before slab cement is poured

This Is What The Homesite Looks Like After The Water & Sewer Pipes Are Installed.

Next The Cement Is Poured To Create The Concrete Slab (Which Sits Over These Pipes)

We Will Discuss Both Slab-Leak Issues:

  • Water Supply-Line needing repair or replacement — due to water-supply pipes that are starting to fail due to age.
  • Water Supply-Line needing repair — due to damage caused by Slab-Movement.

Here Are Signs That You May Have a Water-Supply Pipe Slab Leak

  • Water bill will suddenly spike above your typical usage.
  • Water pressure appears to have dropped.
  • Damp or molded carpet.
  • Bucked or cupped laminate or hardwood floors.
  • Cracks have recently occurred in tile floor covering.
  • Cracks in your walls or the trim near the floor.  This is from upward slab movement due to expansive-clay soil (under the slab) getting more and more wet and expanding in size.
  • Interior doors that stop closing right, stick or bind.
  • A musty odor (it’s likely mold or mildew caused by excessive moisture).
  • There is a puddle of water on the floor inside the home.
  • There is a puddle of water in the lawn right against an exterior wall of your home.
  • You might be able to hear water movement sounds or hissing.

If The Slab Leak Is On A Hot Water Line:

  • You are suddenly running out of hot water when consumption has not changed.
  • Water heater is running more than usual, or it always running.
  • Somewhat increased energy bills.
  • Warm spots in the floor.
  • In winter, a cat or dog is spending time in a new location (they found the warm spot).


You Can Likely Determine If You Have A Water-Supply Pipe Slab Leak

These Steps Should Tell You If You Have A Slab Leak:

  • Be sure all water faucets (inside and outside) are turned off
  • Locate and watch the water meter.  It’s typically inside a green colored box near the curb at the street in front of your home.
  • NOTE: These boxes often require a special too to get the top off.  You may have to call the City to open the box.
  • If the meter’s red needle, or its red “gear” it’s moving, you have a leaking water pipe causing the slab leak
  • The water meter’s red needle and red “gear” display even small amounts of water usage.

city water meter box at the street's curb

city water shut off box

in ground water meter dial


Slab Leaks Must Be Repaired As Soon As They Are Discovered In Order To Prevent Damage To The Slab Foundation Of Your Home

Slab leaks are not something to be ignored, or dealt with later.  The water added under your home (from the leak) will cause the expansive-clay soil under the house to increase in size as it soaks up water.  As this occurs, the soil below your home will exert more and more upward pressure on the slab. Over time, the increasing upward pressure can damage the slab.

Once the leak is repaired, the soil below the home starts to dry out.  As the soil dries and shrinks, the upward pressure on the slab (from wet soil) will disappear.  If enough water leaked from the pipe, there may have been soil erosion & movement.  This can cause a void under the slab, and the soil can no longer provide appropriate support for the slab at that location(s).


image of slab foundation damage due to soil movement below

Slab Leaks Can Cause Upward Slab Movement (Due To Excess Soil-Moisture) -OR- Downward Slab Movement (Due to Drying Out After Repair & Possible Soil-Erosion)

Here Are Several Examples Of Damage To A Home From A Slab Leak

water on exterior of home due to slab leak

slab leak damage buckled concrete

carpet wet from underneath due to slab leakslab leak damage to carpet





buckled tile due to slab leak

slab leak damage to wood floor

slab leak damage to wood trim at floor





Because water-supply pipe slab leaks are under pressure, they can spray water upward against the underneath side of the slab.  Concrete will “wick” moisture upward into the living space of the home. When this happens, water damages everything nearby.

A Vapor-Barrier 

mold due to slab leak

Under The Slab Minimizes Water-Vapor Coming Upward Through The Slab Into The Home

vapor barrier shown under slab


In many Texas municipalities, a vapor barrier under the slab is required by Building Code. This is to minimize the cement’s ability to allow water-vapor upward through it, and into the house.  With a vapor-barrier, the home would be much more humid inside during summer.  Increased humidity also increases the risk of mold.

This same barrier can slow the drying-out process after a slab leak, as only some of the water can be absorbed into the soil.  As long as water (from leak) is under the slab, water will continue to evaporate and water-vapor continues to move upward through the slab.

  • Here Is A Statement From The City Of Rowlett, TX Regarding New Slab Construction.  “Slab sub-grade shall be minimum 4” of compacted sand with 6-mil poly vapor barrier“.

Source:   (Page 9 of 14)

  • This Is The Manufacturer’s Description Of A Common Vapor Barrier:

Vapor Barrier Underlayment prevents vapor from seeping into the home. Designed for residential use, it can be installed at, below or above grade.


How Water-Supply Pipe Slab Leaks Are Repaired

Find The Leaking Water-Supply Pipe

  • The home’s water supply is shut off
  • Air is forced into your water-supply pipe to remove any remaining water.  Then only air is escaping through the crack in the pipe.
  • The location of the leaking pipe may be found by using a very sensitive listening device.  It locates where air is flowing out of the break in the pipe.


Access To The Pipe Must Be Created

There Are 2 Ways To Create Access:

Busting Through The Slab From Inside The House

cut through slab to fix slab leakcut through slab to fix slab leak

A hole is cut through the slab from inside the house.  Jack-hammers break away the cement and soil is set aside.  Once the work is done, the soil is returned to the open area. Then a cement patch is poured to cover the opening.

Issues With Busting Through A Slab For Slab Leak Repairs:

  • In most cases, residents will have to move out of the room, or the entire house.
  • If the work can be contained to one room, there are still times when a resident won’t want to be there, such as when jack-hammers are operating.
  • Floor coverings are often destroyed.  If floor coverings are glued down (like tile or hardwood) they must be destroyed to gain access.
  • The home is exposed to any mold spores or gasses trapped under the slab.  For a sewer pipe slab leak, the home is exposed to bacteria and germs in sewage.
  • Busting through the slab often requires the metal supports (rebar) inside the slab be cut through too.   A slab was designed and constructed as 1 piece, it was never intended to be breached.

Newer homes have Post-Tension Slabs.  If Your Home Has A Post-Tension Slab, A Warning Is Stamped Into The Slab Somewhere Visible (Usually In The Garage)

  • If cutting through this type of slab, extreme care must be taken to avoid (and not cut through) the high-tension cables inside the slab (these cables are visible in the photo below).
  • If a cable is severed, it retracts violently toward the outside edges of the home (the cable was under tremendous inward-pressure).  Severed cables have been known to create damage inside the home during contraction.  There are also documented cases of injuries or death caused an uncontrollable, violently contracting cable.

post tension slab during construction

Post-Tension Slabs Come With A Warning Stamped Into The Cement Telling Not To Cut Or Drill.

Home Builders Stamp This Warning Into The Concrete So They Are Not Held Liable For:

  • Damage to the home’s interior if a cable is severed
  • Possible structural-integrity issues with the slab due to having a cable severed
  • Injury or death of a person in the area where the cable was severed


Tunneling Under The Slab From Outside The House

tunneling under a slab foundation homephoto of tunnel under slab tunnel under slab to sewer pipes









Starting at an outside edge of the home, a tunnel is dug under the slab until the pipes needing repair/replacement are exposed

Benefits Of Tunneling Under The Slab

  • Residents usually can live in the house while the work is done.
  • There is no mess inside the house.
  • No attached floor-coverings are destroyed.
  • The home does not have exposure to anything toxic under the slab (such as mold or gasses).
  • The slab is never cut.  The slab remains in one piece, just as it was: designed, built, and intended to always be.


Why You Must Minimize Your Home’s Slab Foundation’s Movement

In many cases, a slab leak could have been avoided if the soil-moisture level around the edges of the house was kept fairly consistent.

DFW is built on expansive-clay soil.  When the clay in the soil gets wet, it increases in size.  This creates an upward pressure underneath your home’s slab, causing the slab to move upward primarily along the edges and corners.

  • When the soil is too wet, upward force occurs mostly at the edges and corners of the slab (caused by the soil around the edges of the house increasing in size).
  • When the soil is too dry, the soil shrinks (it can turn into dust if it gets dry enough).
  • When the soil is too dry, there is insufficient support from the soil around the edges of the home, and the slab can experience uneven downward pressure (from the home’s weight).
  • The slab does not move evenly because soil moisture-level is more stable farther inward under the slab than at the edges and corners.


This diagram shows what happens to DFW homes’ slabs during changing soil moisture-level.

diagram of slab foundation movement on expansive soils with moisture changes

A slab foundation does not move evenly.   The movement at the edges and corners of the slab is greater than farther toward the center of the slab.  This occurs when the soil around the home becomes too wet and expands -or- dries out and becomes smaller.  The farther toward the center of the slab, the less the soil moisture-level varies.  Since the majority of the changes in moisture-level occur at the corners and outside edges of the slab, the slab’s movement is greater at the edges and corners.

How Slab Movement Damages Water Supply Lines and Waste Pipes

The photo below will help you understand why slab movement can break water supply-lines or waste lines. The horizontal waste pipes are under the slab and run through the soil under the house.  The vertical pipes go up through the slab where they are connected to plumbing fixtures above the slab.

When the slab moves up or down (due to soil moisture-level changes):

  • The vertical pipes (attached to plumbing fixtures inside the home) move up and down with the slab.
  • The horizontal pipes don’t move (because they are located within soil).
  • If the slab movement is enough, the pipes can crack due to the upward or downward pressure the slab-movement creates on the pipes.  The older the pipes become, the more likely they are to fail under slab-movement pressure
  • NOTE: This same movement is also what creates the need for many foundation repairs in DFW.

photo of water pipes coming up from the ground before slab cement is poured

This photo shows both Waste Pipes (white) and Water-Supply Pipes (red & blue) coming out of the ground (under what will be the slab floor when cement is poured)

tunnel under slab to sewer pipes

This photo shows how the sewer-main pipe (largest one) runs through the soil.  It’s exposed in the photo only because of the tunnel that was dug.

One Of The Most Important Maintenance Tasks For Your DFW Home Is To Ensure The Moisture-Level At The Edges Of Your Home’s Foundation Stays Fairly Consistent

The less change in moisture level, the less slab movement, and the less likely you will have: cracked water supply-lines (slab leak), cracked waste lines or foundation damage.

Two Things You Must Do To Minimize Slab Movement Due to Soil Moisture-Level Changes

1. Eliminate Rain Water Falling Off The Roof At The Edges Of The Foundation (to minimize large increases in soil moisture-level).

  • This is accomplished with Rain Gutters to catch and move the water away from the foundation.  Allowing rainwater to fall right at the foundation causes tremendous changes in soil moisture-level. The more the moisture-level changes, the more the slab moves.
  • It’s equally important to have Gutter Downspout-Extensions to carry the water at least 3 feet away from the foundation.
rain gutters installed on a home
Rain gutters on the roof.
rain gutters extension installed on a home
Extensions at the ground.                

2. Provide “Foundation Watering” During Periods Of Hot & Dry Weather (to reduce large decreases in soil moisture-level). 

It’s important to “water” the foundation of your DFW home when the soil around the home is too dry (this is mostly during summer).   This reduces the chances of damage to the foundation, water supply lines & waste lines due to slab-movement caused by low soil-moisture around the edges of your home.   Many automatic irrigation (lawn sprinkling) systems are designed to water the foundation (if it was part of the original installation).

For those who don’t have and automatic irrigation system, an easy way to help maintain moisture-level around your home with with Soaker-Hoses connected to Automatic Timers.

weeper hose in use

These hoses add small amounts of water over long periods of time.  This allows the soil around your home to absorb the moisture.

weeper hose

There Are Many Brands Of Soaker-Hoses.  They All Work The Same Way, So Brand Does Not Matter.


water timer for garden hose

There Are Countless Brands & Styles Of Battery-Operated Timers Available For Garden Hoses.  They Connect To A Home’s Exterior Faucets

3. How Long Do You “Water The Foundation”?

If You See A Gap Between The Foundation And The Soil, You Need To Water That Area Of The Foundation.  The amount of water needed changes from side to side of the home due to sun exposure.  East and north exposures are cooler and require less water than west and south exposures.  If the home is elevated above the ground at the foundation, or is on a homesite that’s on a hill, this also affects how much water is needed on each side, as some homesites drain water away better or less than others.  There are also other factors which affect the frequency and quantity of watering needed.

Your lawn will tell you when it’s too dry around the foundation. Walk around your house and look where the soil is against the foundation (you may have to pull back plants or mulch).

  • If you see a gap between the foundation and the soil, you need to water the ground around your foundation until the soil swells and closes the gap.
  • If you do not see a gap between the soil and foundation, the soil moisture is ok and no watering is required.
  • Lay soaker-hoses 18 inches away from the foundation.
  • Start by setting the water-timer for 2 hours each day.
  • Check each day for a week to see when the gap closes.  That tells you how many days each week you need to water (at that time of the year).
  • Space the days you need to water over a 7-day period.
  • As the weather gets hotter and drier during the summer, you will likely need to increase the number of days you water.  Once each week, check to ensure the gap in the soil does not exist.
  • The best time to water is at night as there is no sun, and cooler temps reduce the amount of evaporation.
  • Most (if not all) municipalities allow foundation-watering at any time on any day.  Check your City’s website to ensure you are in compliance if foundation-watering restrictions apply.

gap between soil and foundation means soil is too dry

A Gap Tells You The Soil Is Too Dry

This information is found in the article “Foundation Watering Tips, Texas A & M University”.  Author: Dotty Woodson, Water Resource Program Specialist, Texas A&M AgriLife Extension Service This link takes you to the article:  Foundation Watering Tips, Texas A & M University


This article addresses slab leaks caused by a damaged water-supply pipe.  The two primary reasons a crack occurs in a water-supply pipe are 1. movement of the slab foundation and 2. pipes failing due to age.

The article also describes how water-supply pipes slab leaks are located and repaired.  Also, access to the pipes needing repair is discussed as 1: busting through the slab for access or 2: tunneling under the slab to gain access to the pipes where they are in need of repair or replacement.

Also discussed are Post-Tension Slabs.  This style of slab construction has been the standard in DFW for new homes built since the 198o’s.  Building a post-tension slab is not typically dictated by Building Code, rather a choice for home builders because they are less expensive to build and post-tension slab strength is notably increased due to the inward compression (in all four directions) of the cables inside the slab.

Post tensioning compresses concrete, enabling it to resist both shrinkage cracks plus cracks caused by difficult soil conditions. Steel strands are run through the concrete in a grid pattern. Each strand is housed inside plastic tube that allows the steel cable to move during the stressing (tightening) operation.  The combination of the steel strand and anchorages is called a tendon. As each tendon is pulled tight, the steel stretches and is held in place by the anchorage on the outside edge of the slab.  The tight tendons help the slab resist forces that act to pull it apart.

Post tension slabs are not designed to be cut through.  If during the cutting a cable is cut, the results can be damaging to the slab, and the notable chance of bodily injury or death is present due to the violent contraction of the cable toward the outside edges of the slab.  Post-Tension Slab homes have a warning stamped into the concrete not to cut or drill into it.  It is possible to cut through a post-tension slab — by first locating the tendons and cutting between them.  The photo below shows and example of this being done successfully.

cutting through post tension slab

Also discussed in this article is another option to gain access to pipes below the slab is tunneling under the slab.

This leaves the slab intact as it was designed, built and intended to always be.

Lastly, the article details how to minimize slab movement due to changes in moisture level.  It’s a simple and tremendously important home-maintenance task for DFW area homes, due to DFW being built on expansive-clay soil.  This clay increases and decreases in size with changes in soil-moisture level.  This causes the slab to move up or down due to pressures created by the soil underneath the home.

DFW homes are built on what is called “floating slabs”.  These slabs are designed to accommodate minimal movement without damage.  The only water to minimize slab movement is to keep soil moisture levels consistent at the outside edges of the slab (moisture level stays increasing consistent father toward the center of the house).


Al’s Plumbing, Heating & A/C performs Slab Leak Detection and Repairs.  Due to the many benefits of tunneling under the slab (versus busting through it) Al’s chooses this preferred method to gain access to pipes needing to be repaired or replaced.

Al’s provides full-service plumbing, heating and air conditioning services.  This includes maintenance, repairs and replacements as needed to restore your home to its correct state. Al’s provides 24/7 Emergency Service for both Plumbing and HVAC (heating, ventilation and cooling) Systems.   Al’s repairs all brands of water heaters, air conditioners, heat pumps and gas & electric furnaces.  Al’s sells and installs Rheem Professional-Grade Water Heaters.  We also sell and install new HVAC Systems from: American Standard (same company as Trane), Ameristar (value-priced HVAC Systems from American Standard) and Coleman HVAC Systems.

Call Al’s today to discuss any plumbing or HVAC problem you have.  We send Texas Licensed Plumbers and NATE Certified HVAC Technicians to get your home back to tip-top condition right away.