Slab leaks usually come from one of a few causes. Pipes corrode from the inside or outside, they rub against concrete or gravel as the house and ground move slightly, water pressure stays too high, or the original installation left a weak spot. Chemistry in the water and the type of pipe both affect how fast any of this happens.
Rarely is it one thing alone. A pipe with a small flaw from installation will fail sooner if pressure is high and the soil moves. We do not know the foundation or pipe type of your specific home from the address alone, so this guide speaks in general terms, and a plumber should confirm what you actually have.
The short list of reasons pipes under a slab fail
These are the causes plumbers talk about most. The table shows how each one works and what clue it tends to leave.
| Cause | How it damages the pipe | Clue you may see |
|---|---|---|
| Corrosion | Water and minerals slowly eat through metal pipe walls from inside or from the soil side. | Pinhole leaks, green or blue stains on copper, repeat repairs in the same line. |
| Abrasion | A pipe vibrates against concrete, rock or another pipe until the wall wears thin. | Leak near a bend or a spot where the line passes through the slab. |
| Shifting or settling ground. | Soil movement puts stress on rigid pipe and joints. | New cracks in slab or walls along with a leak. |
| High water pressure. | Constant stress stretches fittings and weak points. | Banging pipes, short-lived fixtures, relief valve weeping. |
| Installation flaws | A kinked pipe, rough cut edge or poorly made joint starts a leak later. | Leak close to a fitting or elbow. |
| Scale and mineral buildup. | Deposits restrict flow and can speed wear at turns in the pipe. | Falling flow, noisy lines, scaled aerators. |
| Outside forces | Nearby digging, heavy loads or root pressure can damage a buried line. | Leak after work in the yard or a change in the ground above the line. |
Corrosion: the slow cause
Metal pipe slowly loses wall thickness. Water chemistry matters, and so does the soil around the pipe. Acidic or mineral-rich conditions can attack copper from the outside, while water running through a line can wear it from the inside.
This is why leaks tend to appear at the same age across a whole house. One pinhole is often the first of several, because the rest of the line has had the same exposure. A single repair may buy time, but if several spots are thin, ask the plumber whether repiping the affected section makes more sense than patching one hole at a time.
Does the ground under my house move?
Any slab can shift a little as soil dries, gets wet, or settles. Pipes that pass through the concrete need room to move, and when they do not have it, they can fray at the point of contact.
Arizona has a particular geology story. The Arizona Geological Survey reports that land subsidence and earth fissures from groundwater pumping affect parts of Maricopa County. That is a county-wide fact and not a statement about El Mirage. We cannot tell you whether your lot has any such movement, so do not assume it, and look to cracks in the slab or walls as the practical signal.
If you see new cracks along with signs of a leak, mention both to the plumber. That helps decide whether the leak caused the movement or the movement caused the leak.
Want a plumber to look at it?
Call the 24/7 line, describe what you found and hear a clear price before work starts.
Pressure, hardness and the pipes themselves
Two forces work on pipe all day. One is how hard the water pushes, and the other is what the water carries.
Pressure
- High pressure stresses every joint and fitting.
- Signs include hammering pipes and a relief valve that drips.
- A plumber can measure it with a gauge on a hose bib.
- A pressure regulator, if one is installed, can wear out.
- We do not have a published pressure figure for El Mirage, so measure yours.
Water chemistry and scale
- Hard water leaves mineral scale on fixtures and in heaters.
- Scale in a buried line is hard to see and not always a factor.
- Hardness is a general scale factor here, not a proven cause of slab leaks.
- A softener changes the scale picture but does not repair existing damage.
- Pipe type and age often matter more than hardness.
What was built in, and what nobody has checked
The pipe in your slab was chosen and installed when the house was built. Materials, depth, wrapping and the way fittings were made all vary between builders and eras. A bend that was forced into place, a pipe that touches rebar, or a joint made in a hurry can be the weak point for decades before it gives out.
Houses of the same age can still differ. That is why the first useful question for a plumber is not what usually fails, but what is in this house and how it was routed. Ask to see the shutoff, the regulator if you have one, and the likely path of the water line.
What you can influence, and what you cannot
You cannot rebuild the pipe layout, but several habits reduce stress on the system.
- Have the pressure measured once, and ask what the number should be for your fixtures.
- Replace a failed pressure regulator rather than living with hammering pipes.
- Fix small drips early so they do not hide a larger problem.
- Do not pour drain chemicals into lines that already leak.
- Call 811 before you dig for a fence, a pool or a sprinkler line, since utilities have two full working days to mark their lines.
- Write down repeat repairs, because a pattern points to a failing line.
- Ask the plumber what pipe material you have, and note it for the next owner or repair.
A leak and a cause are two different questions
Finding where a slab leak is does not prove why it happened. Some plumbers can see the failed section and describe what they find. Others can only say where it is.
Ask what the cut-out piece looked like. A pinhole with pitted metal tells a different story than a split from a hard bend. Our page on slab leak repair covers what happens after the cause is known.
What we know and do not know about El Mirage homes
Census-based data suggests the median El Mirage home was built around 2004, and most homes date from the 2000s boom. That points to newer tract construction, but it does not confirm the pipe type or foundation in any one house. Ask the plumber to confirm what is under yours.
The city's 2024 water quality report lists hardness from 4 to 9 grains per gallon, with an average of 7. That makes mineral scale a general factor to keep in mind for heaters and fixtures. Check the latest report for current numbers.
Parts of Maricopa County have land subsidence and earth fissures, according to the Arizona Geological Survey. We make no claim that El Mirage does, and the survey page does not say so. If you suspect ground movement, your cracks and your plumber's findings are better evidence than a county map.
Frequently asked questions
Age matters mainly because metal pipe wears over time. A newer house can still have an installation flaw. Age is a clue, not a rule.
Hard water leaves scale in heaters and fixtures, and it can add wear in some systems. It is a general factor and not a proven single cause. Pipe material, pressure and installation quality usually carry more weight.
Not always. Slabs crack for many reasons, and most small cracks are cosmetic. A crack plus damp flooring or a moving meter is the combination that deserves a plumber's visit.
No. You can reduce stress by checking pressure and fixing small leaks, but you cannot see or reach most of the pipe. Early detection through the water meter is your best protection.
We cannot say that. Fissures from groundwater pumping affect parts of Maricopa County according to the Arizona Geological Survey, but that is a county-level fact and not a finding about El Mirage. Use your own evidence and ask the plumber what they see.
Question not answered here? Call (623) 301-9042
Sources and code notes
Code reference: El Mirage follows the 2018 International Plumbing Code (IPC) and the 2018 International Fuel Gas Code (IFGC). Ask the El Mirage building department which rules and permits apply to your job. Hardness figures come from the City of El Mirage 2024 water quality report. Dig-safety timing comes from Arizona 811, which the Arizona Corporation Commission oversees.