Short answer
How do you know if you have a slab leak?
The usual signs are a warm patch on the floor and the sound of running water with every tap closed. Add a water bill that climbed without a change in habits, or damp carpet in one spot. Any one alone can mean something else. Two together usually means a slab leak.
A slab leak is a break in a water line that runs inside or underneath the concrete foundation of your house. Most of them start on the hot water side, because hot copper moves more and corrodes faster. The water has nowhere to go, so it soaks the soil under the slab, then finds its way up through the concrete.
The important part is the locate. A plumber who guesses opens more floor than the repair needs. A plumber who uses acoustic listening gear and a pressure test on each line can usually mark the spot to within a foot or so before anything gets cut.
Warning signs worth acting on
- A warm or hot patch on a tile or vinyl floor, often near a hallway or a bathroom wall
- Running water sounds when every fixture in the house is off
- A water bill that jumped by a third or more with no change in use
- Carpet that stays damp in one area, or wood flooring that cups and lifts
- A musty smell in one room that doesn't clear with airing
- Low pressure at fixtures that used to run fine
- Hairline cracks appearing in floor tile or along a wall base
- The water meter dial still creeping when the main is the only thing running
What to do before the plumber gets there
- Turn off every fixture, then look at the water meter. If the low-flow dial is still turning, water is escaping somewhere between the meter and your fixtures.
- Shut the water off at the main if the floor is actively wet. The main shutoff is usually in a box near the street or on the side of the house near the hose bib.
- If the warm spot is on the hot side, close the cold inlet valve on top of the water heater. That isolates the hot loop and tells you a lot in ten minutes.
- Move furniture and rugs off the damp area so the floor can dry and nothing else gets ruined.
- Photograph the damp area and keep the last two water bills. If you end up filing an insurance claim, that's the evidence that matters.
How the job is done
Isolate the line
The plumber closes valves section by section and watches the meter. That separates a hot side leak from a cold side leak and rules out irrigation, which is a common false alarm in Orange County yards.
Pressure test
Air or water pressure goes on the suspect line with a gauge attached. A line that holds pressure isn't your problem. A line that bleeds down is.
Locate acoustically
Ground microphones and a line tracer narrow the leak to a small area of floor. Thermal imaging helps on the hot side. Expect this to take an hour or two on a typical single story house.
Choose the repair
Three options are normal: open the slab and fix the spot, reroute that line overhead or through walls, or repipe the house if the pipe is failing in several places.
Repair and restore
A spot repair means cutting concrete, fixing the pipe, pressure testing again, then patching. Ask in writing who is responsible for the floor covering afterwards, because that's the most common surprise on the invoice.
What it typically costs in Orange County
Detection and repair are usually two separate line items. Plenty of companies credit the detection fee against the repair if you use them for both, so it's worth asking.
| Job | Typical published range |
|---|---|
| Slab leak detection | $150 to $600 |
| Slab leak spot repair | $1,500 to $3,500 |
| Rerouting the line instead of opening the slab | $2,000 to $5,000 |
| Whole house repipe in PEX | $4,000 to $8,500 |
Estimates, not quotes. Ranges below were compiled in September 2026 from published Orange County contractor price guides and national 2026 cost data. They're a starting point for comparing written quotes, not a quote.
What moves the price
- Whether the leak sits under a slab edge or in the middle of a room with tile over it
- Hot side versus cold side, since hot lines often fail in more than one place
- How much concrete has to come out, and whether the floor covering can be saved
- Whether a reroute is cheaper than a spot repair, which it often is on a second failure
- Restoration, which many plumbers exclude from the quote entirely
What you can do yourself, and what needs a pro
Worth trying yourself
- Run the meter test yourself. It costs nothing and tells the plumber something useful before arrival.
- Isolate the water heater to separate hot from cold.
- Clear access to the suspected area and to the main shutoff.
Call a licensed plumber for
- Any cutting of the slab, which needs the rebar located first
- Pressure testing, because an over-pressured domestic line can split somewhere new
- Deciding between spot repair, reroute and repipe, which depends on the pipe condition the plumber can see
- The permit, which the city expects on a repipe or a water service alteration
This isn't a worth-a-try job. Every hour a slab leak runs it adds to the soil saturation under your foundation, and the repair doesn't get cheaper.
Local context
Why Santa Ana gets so many of these
Santa Ana built out heavily in the post-war decades, and the tract housing from that period sits on slab-on-grade foundations with copper supply lines run inside the concrete. That construction method was normal and legal. It just means the pipe isn't reachable without opening the floor.
The water here is hard. The city puts it at roughly 250 parts per million, around 15 grains per gallon. Hard water combined with decades of hot water cycling is what produces pinhole failures in thin-wall copper, and the hot line almost always goes first.
One local company in Orange County has built its entire business on slab leaks and in-place pipe restoration. That tells you how common the problem is here. It also means you should get a second opinion before agreeing to a whole-house solution on the strength of one leak.
Keeping it from happening again
- Keep house pressure at or below 80 psi. High pressure shortens the life of every joint in the slab.
- Have the hot line checked after the first repair. A second pinhole within a year usually means the run is finished, not unlucky.
- Watch the meter once a month. Two minutes with every tap closed catches a small leak while it's still small.
- Treat the hard water. A softener or a scale reducer slows internal corrosion across the whole system.
- Don't ignore a pressure drop. Losing pressure over weeks is a leak behaving exactly as a leak behaves.
Where we send plumbers for this
Coverage runs across Santa Ana, Tustin and Fountain Valley. Some areas have a page of their own, because there is enough genuinely different about them to write down.