The first clue is usually a water bill that climbs even though nothing about how your household uses water has changed. The pipe responsible is buried under your concrete foundation, where you can’t see what’s happening.
A slab leak is a crack, hole, or failed connection in a water supply or sewer pipe running beneath a home’s concrete slab. Because the pipe is hidden, you almost always notice the effects before you find the leak.
Most homes in Gilbert, Chandler, and Mesa sit on concrete slabs, and finding and fixing slab leaks is part of what we do across the East Valley. They rarely have a single cause. Aging pipe, shifting soil, water chemistry, and too much pressure work on the same stretch of pipe for years until the weakest point gives. You can’t control all of that, but you can control pressure, water quality, and drainage, and we’ll cover all three.
Key Takeaways
- Older homes with original galvanized steel, cast iron drain lines, or aging copper face the highest risk. Galvanized steel and cast iron are especially prone to corrosion, and older copper can develop pinholes or be damaged by soil contact.
- The International Plumbing Code and Uniform Plumbing Code both require an approved pressure-reducing valve when static water pressure exceeds 80 PSI.
- To check for a hidden supply leak, turn off everything that uses water, record your meter reading, and check it again an hour later without using any water.
- Repair cost depends mostly on where the pipe sits, how much of it needs work, and how much concrete and flooring has to be restored afterward.
What Is a Slab Leak?
Two kinds of pipe can leak under a slab. Pressurized supply lines bring hot and cold water into the house, and sewer and drain lines carry wastewater out, usually by gravity. They give themselves away differently. A leaking hot water line may leave a warm spot on the floor, while a damaged drain line may cause odors or moisture problems, sometimes before there’s any visible damage.
A slab leak starts as a plumbing problem, not a foundation problem. But if escaping water keeps soaking the soil that supports the slab, foundation damage can follow. The goal is to catch it while it’s still a pipe repair.
Common Causes of Slab Leaks
A pipe under a slab rarely fails for one reason. More often, it’s already been weakened by age or corrosion when changing soil conditions or water pressure finally push it over the edge.
Pipe Corrosion and Age
Copper is durable, but it doesn’t last forever. Aggressive water chemistry can pit it from the inside until the wall is thin enough to open a pinhole, and copper buried against soil without proper protection can corrode from the outside too. Even a small opening wastes a surprising amount of water. At around 60 PSI, a large enough pinhole can release several gallons an hour, depending on its size.
Galvanized steel and older unlined cast iron are even more vulnerable. Cast iron is generally used for drain and sewer lines, while galvanized steel shows up in older water supply systems.
Many East Valley homes built from the 1970s through the early 2000s have copper under their slabs, and those lines have now been in service for decades. That doesn’t mean every one is about to fail, but age, installation, and water chemistry deserve a close look when a leak shows up. Newer homes often use PEX for supply lines, which avoids the corrosion problems of metal pipe.
Pressure and Water Quality
High water pressure doesn’t usually burst a pipe outright. It works on the line constantly until it cracks at the weakest point, which is usually a fitting, joint, or soldered seam rather than a straight run of pipe.
Water chemistry matters too, but hardness and corrosion aren’t the same thing. Hard water carries extra calcium and magnesium, which leave scale inside pipes, fixtures, and water heaters. Corrosion depends on other conditions, including pH, dissolved substances, temperature, and pipe material.
East Valley water is often hard to very hard, commonly around 10 to more than 20 grains per gallon depending on the utility, neighborhood, and blend of groundwater and Central Arizona Project water. That alone doesn’t make it corrosive, though. Your utility’s annual water quality report lists pH and may list hardness, although hardness isn’t a regulated health contaminant.
The EPA’s recommended secondary pH range for drinking water starts at 6.5. Water below that may be worth checking for corrosivity, but pH is only one part of the picture.
Ground Movement and External Damage
Expansive clay soils occur in parts of the Phoenix metro area, including Gilbert, Chandler, and Mesa. Clay swells when it gets wet and shrinks as it dries, and monsoon storms after long dry stretches push it through that cycle hard. Pipes in moving soil can bend, shift, or pull at their connections until a weakened line cracks or separates. Summer heat adds a little more movement as the pipe expands and contracts.
Installation matters just as much. A line resting against sharp gravel, concrete, or rebar can wear through as it moves, which is what proper bedding, sleeves, and protection are meant to prevent. Once the concrete is poured, none of that is visible, and the damage can go on for years before anything shows.
How to Spot a Slab Leak
The earlier you catch a slab leak, the less damage it does. None of the signs below proves a pipe under the slab is leaking on its own, which is why we always confirm the source before anyone cuts into concrete.
Visual and Physical Signs
Floor temperature tells you a lot. A warm patch can mean a leaking hot water line, since escaping hot water heats the concrete above it. A damp or cool area may point to a cold water leak, a drain problem, or another source of moisture.
Cracked tile, damaged hardwood, new cracks in interior walls, and doors that suddenly stick can show up once leaking water has changed the soil under the foundation. All of these can have causes unrelated to plumbing, so look for a combination of clues. They also tend to appear later, so the water bill and sound clues below are usually better early warnings.
Water Bill and Sound Clues
If your household hasn’t changed its habits but your water bill has gone up, water is escaping somewhere. You might also hear faint hissing or running water with every faucet and appliance off, which can point to a pressurized supply leak, although it won’t tell you where.
The meter test takes an hour:
- Turn off all faucets, showers, appliances, irrigation, and anything else that uses water.
- Write down the reading on your water meter.
- Wait one hour without using any water, then check it again.
If the meter has moved, water is flowing somewhere. That suggests a leak but doesn’t confirm one under the slab, since a running toilet or an irrigation leak can do the same thing. If you can’t find the source, that’s the point to bring in professional leak detection.
Professional Detection Methods
Finding a slab leak doesn’t mean tearing up your floor to look for it. We use several methods to narrow down the location and confirm which line is leaking, because opening the slab over the wrong pipe is an expensive mistake.
| Method | How it works | Best for |
|---|---|---|
| Acoustic listening | Amplifies the sound of water escaping under pressure; checking different spots narrows down the area | Pressurized supply leaks (accuracy depends on the pipe, leak size, materials, and background noise) |
| Thermal imaging | An infrared camera picks up temperature differences across the floor | Hot water line leaks, which can show as a warmer area |
| Pressure testing | Isolates sections of plumbing to see which one is losing pressure | Confirming whether the hot or cold supply has the leak |
| Video camera inspection | A camera checks accessible drain piping for cracks, offsets, corrosion, and roots | Sewer and drain lines |
It usually takes more than one. One test points to the likely area, and another confirms the pipe. That extra step is what keeps us from opening concrete we didn’t need to touch.
Repair Options and What They Cost
Not every slab leak means breaking through your living room floor. The type of pipe, the extent of the damage, and what can be reached safely decide the repair method, and the method drives most of the price and timeline.
Trenchless Repair Methods
Pipe lining is an option for certain damaged drain and sewer lines. A resin-coated liner is placed inside the existing pipe and cured to form a new interior surface, which cuts down on digging. But a liner can only seal what’s structurally still there, so severe collapse or extensive deterioration may rule it out. Lining drain lines is also a different application from repairing pressurized water supply pipes, with different requirements.
Rerouting is the usual approach for leaking supply lines under a slab. Instead of opening the concrete, we take the damaged run out of service and install a new PEX or copper line through accessible walls, ceilings, or the attic, depending on the installation and code requirements. In an older home with deteriorating under-slab copper, a reroute often makes more sense than patching one pinhole after another. That’s a call we make after inspecting your system, not before, and if a single spot repair will do the job, we’ll tell you so.
Traditional Excavation and Repair
Sometimes the pipe has to be reached directly. Under-slab tunneling digs in from outside the house, which can preserve interior flooring, but it’s labor-intensive and may need extra precautions to protect the structure.
For a localized leak in an accessible spot, the other option is going in from above: cutting through the flooring and concrete, repairing the pipe, and patching the opening. The plumbing part is often simple. The restoration usually isn’t. Tile, hardwood, or carpet may need to come out and go back in, and matching older flooring can be the hardest part of the job. That’s why a small leak doesn’t always mean a small bill.
Cost Range and Timeline
| Type of work | Phoenix-area planning range |
|---|---|
| Leak detection | Around $150 to $500 or more |
| Spot repair involving concrete access | Roughly $800 to $2,500 |
| Single-line reroute | Around $1,200 to $5,000 or more |
| Extensive excavation, multiple-line replacement, or major flooring restoration | Higher, depending on scope |
These are broad planning ranges, not fixed prices. Three things move the final number most:
- Access, especially when the leak sits under finished flooring or a difficult structural area.
- Pipe condition. If the surrounding plumbing is badly deteriorated, fixing one opening may not solve the bigger problem.
- Restoration. Flooring and concrete work can add substantially after the leak itself is fixed.
A simple reroute or contained repair may take about one working day, with water back on the same day. Tunneling, extensive excavation, and flooring restoration can take several days or longer, and most of that time goes to restoration rather than plumbing.
Detection may be billed separately from the repair, so ask what’s included and whether restoration is part of the quote. With us, you’ll know all of that before work starts, and the price we quote is the price you pay.
Insurance Coverage for Slab Leaks
Under a typical HO-3 homeowners policy, sudden and accidental water damage to covered flooring, walls, or belongings may qualify for coverage, but the failed pipe itself is often excluded. In other words, the damaged drywall and flooring may be covered, while the plumber’s invoice for fixing the line usually isn’t. Some policies also have separate provisions for the cost of accessing a damaged pipe.
Insurers also frequently exclude damage that develops gradually over weeks, months, or years, which is one more reason to act on early signs. If you suspect a leak:
- Photograph visible damage before any repairs begin.
- Keep your water bills, especially any that show a sudden jump.
- Ask your plumber for a written inspection report identifying the suspected cause, the affected plumbing, and the date the problem was found. We’re happy to provide one.
Coverage for gradual damage, continuous leakage, access work, and restoration varies between policies and insurers. Read your own policy and talk to your insurer before you assume a repair is covered, not after the adjuster has been out.
Risks of Ignoring a Slab Leak
A small leak under a foundation doesn’t stay small. The longer it runs, the more of the house gets involved, and because insurance may not cover the failed pipe or gradual damage, waiting usually means paying more out of pocket.
Structural and Foundation Damage
A concrete slab depends on the soil beneath it for support. When leaking water changes that soil’s moisture, the ground can swell, soften, erode, or settle unevenly, which can crack the slab, flooring, or nearby walls. On East Valley clay that’s already moving through seasonal wet and dry cycles, a leak adds one more source of water underneath.
If new cracks show up alongside signs of water loss, have the plumbing checked. A meter test and pressure testing can tell you whether a supply leak is present, and a structural engineer should evaluate any concerning foundation movement or cracking.
Mold and Health Concerns
Persistent moisture under flooring or inside walls can lead to mold growth where you can’t see it, sometimes without an obvious musty smell. According to the CDC, mold exposure can cause nasal congestion, throat irritation, and coughing in some people, and it can worsen symptoms for people with asthma or mold allergies. Effects depend on the individual and the extent of exposure. Once moisture has spread into flooring or drywall, fixing the pipe is only part of the job, and those materials may need drying, removal, cleaning, or replacement.
Prevention Tips
You can’t prevent every slab leak, but you can take a lot of stress off your plumbing by keeping an eye on water quality, pressure, and drainage.
How Water Quality Affects Pipe Corrosion and Slab Leaks
Hard water and corrosive water need different treatment. A conventional water softener removes calcium and magnesium to reduce scale, but it doesn’t correct acidic or otherwise corrosive water. Where testing shows a pH problem, a properly selected neutralizing treatment may be the better fit. East Valley water chemistry varies with the source blend, so test before you buy anything. We’d rather recommend equipment based on what’s actually in your water than on a guess.
If you’re planning a major renovation in an older home, it’s also worth having the original under-slab piping evaluated. Replacing deteriorated galvanized steel or vulnerable copper with properly installed PEX or protected copper may reduce the chance of future failures, depending on your layout and the condition of the existing lines.
Pressure, Drainage, and Inspections
Put a pressure gauge on an outside hose bib and check your static water pressure. If it reads above 80 PSI, the code threshold for a pressure-reducing valve, have the pressure and any existing valve checked. A properly working valve is one of the most affordable ways to protect your plumbing.
Keep gutters and downspouts clear, and make sure the ground slopes away from the foundation so monsoon runoff doesn’t collect against the house. Steady drainage limits big swings in soil moisture. On expansive clay, keep an eye out for new cracks or unusual settling, too.
Think You Might Have a Slab Leak?
If your meter is moving and you can’t figure out why, give us a call. We’ll find the leak, confirm which line it’s on before we cut anything, and walk you through your options in plain English, including whether a reroute or a simple spot repair makes more sense for your home. You’ll get a fixed price before any work starts, and the price we quote is the price you pay. Call us at (480) 662-6555 or tell us what you need.
