There are four ways that your plumbing will develop a leak under a slab:

1. Corrosion from soil chemicals
2. Abrasion from long term vibration
3. Pressure from human error or shifting ground
4. Construction defect

Slab leaks from corrosion:

Underground pipes make contact with soil on the exterior of the pipe and water on the inside. Water balance and a charged ground could induce electrolysis in metallic pipes, causing corrosion from the inside or outside of the pipe and eventually causing holes in the pipe.

Hot water lines will more likely corrode from the outside in due to the reaction of the heat and the contents of the soil surrounding the pipe.

Cold water lines generally deteriorate from the inside out due to electrolysis being created on the inside of the pipe.

Electric lines running beneath the slab can also energize metallic pipes and induce electrolysis resulting in corroded pipes.

Older homes with copper pipe usually suffer from chronic plumbing failures due to corrosion. Sometimes the situation calls for a complete repiping of the plumbing. Less invasive repairs can be made with an in-place pipe coating depending on the state of the pipes and the construction layout.

Slab leaks from abrasion:

As water travels through plumbing, vibrations, expansion and contracting may cause the pipe to rub against concrete, gravel, rebar, or other pipes depending on the construction. Over time, the constant vibration and abrasion of the pipe will grate the pipe until it springs a leak.

If pipes are insulated and constructed with stabilizing supports, the vibration can be minimized, prolonging the life of the pipes while protecting if from being exposed to excessive wear.

Additionally, bad joints and lack of coupling adhesion can lead to abrasion at the joints, leading to faster and higher volume leaks.

Slab leaks from pressure:

Underground pipes may experience high levels of pressure from earthquakes, or poor construction. Pipes can be crushed or creased under this type of pressure, depending on the area of pressure. Creased pipes may cause a restriction in flow and low pressure. Additionally, a crease, bend or crimp in the pipe will allow uneven wear and the water will eventually create a hole at the problem areas. Crushed pipes can cause massive leaks over time that wash the soil from under the foundation, putting your property at risk of greater damage.

Pipes need to be spaced and insulated properly in order to avoid being crushed or creased. Many times a crushed or creased pipe can be repaired without a full repipe of the home.

Construction Defect:

During construction, faulty workmanship may not only require rework, but also may result in damage to construction work performed by others.

If you hear running water in your home when all should be quiet, means there is flowing water somewhere.

Your home’s plumbing is pressurized and static when all appliances and faucets are in the off position. The sound of running water is created by the vibration of the flow of water against the piping system. It means an outlet from the system is allowing flow. You will need to check all  faucets, toilets, sprinklers, as well as water connected appliances like refrigerators, clothes washers, dish washers, or water purification systems.

If you don’t find visual clues to the source of the sound of water, it could mean you have a hidden leak in the wall or under the slab.

A hot spot on the floor could indicate a hot water line leak in your slab.

Hot water lines are usually insulated and don’t heat the floor unless it was built as a radiant heating system.

If you have pets, you may notice they gravitate to a certain spot on the floor. Check to see if it feels warmer than usual.

Cracks in walls or floors could be damage from a slab leak.

There are several possible factors in the appearance of cracks in walls and floors. If you live in a seismically unstable area, it could instead have to do with shifting ground due to earthquakes.

Even if ground shifting is due to unstable ground, it could also mean the area under your property has been compromised by  water flow from a leak under your slab. If untreated, a water leak could create a massive void under the foundation. This void can put stress on the foundation, and increased stress on the foundation can cause cracks in the floors and walls.

Mildew or excessive moisture under carpets could indicate your slab is cracked and the pipes inside are leaking.

Cracks in a slab due to a leak allow moisture into the flooring. Drywall will wick the moisture up, and create an ideal environment for mold to grow behind the wall. Mold is an environmental hazard and you need to make sure that proper clean up and restoration of the property is performed. Before the restoration is performed, the mold needs to be removed. Then, the location of the source of moisture that feeds the mold can be identified and repaired.

High water bills could indicate a leak. Although a high water bill could indicate a water leak behind the wall or in your pool, plumbing under the slab is also suspect.

Unusually high water bills could occur for several reasons. Sometimes the meter is not working properly and needs to be replaced. You will need to contact your water authority for this kind of issue.

If your meter is working properly, then it comes down to usage.

Conduct the meter test to see if your toilets are leaking or if you have a hidden water leak.

The wrong way:

The right way: