A slab leak is a break in a water line inside or beneath the concrete floor. Three signs are worth trusting: one patch of floor that feels warm, a water meter that moves with every fixture off, and a bill that stepped up and stayed up. A plumber repairs the pipe; a restoration crew dries the house.
Key takeaways
- The three reliable signs are a warm spot on the floor, meter movement with everything off, and an unexplained increase in the water bill that does not come back down.
- A meter test takes an hour and costs nothing: note the reading with every fixture, appliance, irrigation valve and pool fill off, then read it again.
- A licensed plumber locates and repairs the pipe, and the restoration crew extracts water, lifts flooring that cannot dry and dries the slab; two bills, two schedules.
- Local plumbing write-ups put leak detection in the low hundreds of dollars and a full re-route in the thousands; that is a plumber's work and never part of a cleanup quote.
- Concrete is dense, so a wet slab is specialty drying under the industry standard: sealed mats, heavier dehumidification and more days than carpet or drywall would need.
- Do not lay new flooring until the slab reads dry against a reference elsewhere in the same house, or the second installation is at your expense.
What is a slab leak, and why do they turn up in Phoenix houses?
A slab leak is a failure in a water line run inside or under a concrete floor slab. The escaping water soaks the concrete, spreads sideways along it and rises into flooring, baseboard and the bottom of walls. Houses here are built on slabs, so a buried line is the normal way to run water.
Slab-on-grade construction took hold early in this valley, and the post-war neighborhoods that spread across central and west Phoenix were among Arizona's first large slab developments: a great many single-story houses with supply lines in or beneath the concrete rather than in an accessible space.
What makes the leak expensive is not the hole. It is that the concrete becomes a reservoir and the floor above it a lid. Water travels along the top of the slab under tile and laminate, wicks up into drywall paper and baseboard, and shows up in a room that has nothing to do with the plumbing.
Not every under-slab leak is a pressurized supply line, either. Older cast iron and clay drain lines crack, separate or take on roots, and that water is contaminated rather than clean, which changes what can be kept and how the room is cleaned.
Which signs of a slab leak are actually worth trusting?
Three carry real weight: a patch of floor noticeably warmer than the rest, a water meter whose low-flow indicator turns with everything in the house shut off, and a water bill that stepped up and stayed up with no change in how the household uses water. The rest are hints, not evidence.
A warm spot is the most specific sign there is, because it says the hot-water line is the one leaking and roughly where. Walk the house barefoot on tile in the morning, before sun reaches the floor through a window, and note anything warm in one place and cool a step away.
The softer signs are worth noting and not worth panicking over: running water heard in a quiet house at night, grout darkening in one area, laminate cupping, baseboard swelling along an interior wall, a musty closet, or hot water pressure that has fallen off. Each has several explanations, which is what the table sorts out.
| What you notice | What it usually points to | What else it could be |
|---|---|---|
| One patch of floor warmer than the rest | A hot-water line leaking under the slab | Sun through a window, a water heater closet, a duct run under the slab |
| Meter low-flow indicator turning with everything off | Water escaping somewhere on the property | An irrigation valve, a pool auto-fill, a toilet flapper, an ice maker |
| A bill that stepped up and stayed up | A continuous leak rather than a usage change | A new irrigation schedule, a hotter summer, a pool refill, house guests |
| Wet tile or carpet in the middle of a room | Water travelling along the top of the slab | A shower pan, a toilet seal, a condensate line in a wall, an appliance line |
| Running water heard at night | Water escaping from a pressurized line | A recirculation pump, a pool pump or cleaner, a neighbour's irrigation |
How do I run a water meter test at home?
Shut off every water use in the house and on the lot, write down the meter reading, wait an hour without using water, and read it again. Any change, or a low-flow indicator that keeps turning, means water is escaping somewhere. The test proves a leak exists; it does not say where it is.
The whole value of the test is in how completely you shut things off. The usual spoilers are the ones nobody counts as water use: the irrigation controller, a pool or fountain auto-fill, a water softener in a regeneration cycle, the ice maker, an evaporative cooler with a float valve, a reverse-osmosis unit, and a toilet with a flapper that seeps quietly.
If the meter is still moving after all that, close the house shut-off valve and watch it again. Still moving means the leak sits between the meter and that valve, which points outdoors at the service line or the irrigation system. Stopped means it is on the house side, and the slab is a live possibility.
Then stop and hand it over. Narrowing a leak to a spot in the concrete takes acoustic and pressure equipment and the experience to read it, so it belongs to a plumber rather than to a guess and a saw: cutting a slab on a hunch risks the line beside the one that failed, and the conduit buried with it.
- Turn off every tap, shower, washer, dishwasher and ice maker, and tell the household
- Switch the irrigation controller to off, not to a rain delay, and close any pool or fountain auto-fill
- Photograph the meter face, including the low-flow indicator, so the first reading is not a memory
- Wait at least an hour with nothing used, then photograph it again and compare
What else makes a floor wet in the middle of a room?
Several things that cost far less to fix. A failed shower pan or a leaking toilet seal wets a floor only after that fixture is used. An air-conditioning condensate line running inside a wall drips while the system runs. An irrigation break outside the stem wall soaks in from the yard. Rule those out first.
Timing is the cheapest diagnostic you have. Water that appears after a shower and nowhere else points at a pan or a drain, not a pressurized line. Water that appears on hot afternoons while the air conditioner runs hard points at a condensate drain or pan; the condensate leak service describes that one.
Water that shows up on the morning the irrigation ran, near an exterior wall, is almost always outside work. A broken lateral, a cracked valve box or a flood-irrigation berm that failed can put water against a stem wall and through it, and none of that involves the slab.
Appliance supply lines are the other common lookalike, especially a braided line behind a refrigerator or a washer that has seeped for weeks. A slab leak and a seeping supply line look identical on a tile floor, and only the meter test and a look behind the appliance tell them apart.
Why do these leaks happen in Valley houses at all?
Three things stack up. Tap water here is among the hardest of any large US city, so scale and sediment work on pipes, valves and fittings for decades. Valley soils are desert alluvium with hard caliche layers and pockets of clay, and movement in that ground stresses buried lines. And much of the housing stock is old enough to show it.
Hardness is worth understanding rather than quoting. Published figures from water-treatment vendors disagree with each other, so the honest statement is that Phoenix tap water is classed very hard, and the City of Phoenix Water Services annual water quality report is the authority for your own address.
Ground conditions get blamed for the rest. Caliche is a hard calcium carbonate layer running through valley soils, clay pockets swell and shrink with moisture, and lines buried in that ground take the strain; it is a reasonable explanation rather than a measured cause.
Age is the part that is documented. Maryvale was started in 1954, Alhambra and Sunnyslope filled in largely with post-war houses, Tempe has surveyed roughly 4,500 properties built between 1945 and 1960, Arcadia is mostly 1950s and 1960s ranch houses on old citrus-grove lots, and Sun City's homes date from 1960 on. Mid-century slab houses commonly went in with copper supply lines, but only a plumber who has looked can say what is under your own slab.
Which trade fixes the slab, and who dries it afterward?
A licensed plumber locates the leak and chooses the repair, either opening a small section of slab for a spot repair or abandoning the buried run and re-routing the line overhead. A restoration crew handles extraction, flooring removal, drying the concrete and the documentation. Rebuild work goes to a licensed contractor afterward.
That split is the most useful thing on this page. A plumber fixes the pipe; the crew dries the house. Nobody here does leak detection, slab repair, re-piping or water heater replacement.
Plumbers in the Valley report leak detection at roughly $150 to $500, a spot repair through the slab commonly between about $500 and $2,000, and a full re-route running from a few thousand dollars well into five figures, with an overall spread quoted as wide as a few hundred dollars to about $15,000. Those are their numbers for their own work, taken from local plumbing write-ups rather than from any quote here, and only a plumber who has seen your house can narrow them.
Rebuild work afterward generally calls for a contractor licensed by the Arizona Registrar of Contractors, unless a small job below a state dollar limit applies. Cleanup pricing for the water side sits in the Phoenix water damage cost guide, where slab leak cleanup for one or two rooms is estimated at $1,200-$5,000 with the plumber's work excluded.
- Plumber: detection, spot repair, re-route or partial repipe, pressure testing, water heater work
- Restoration crew: extraction, wet flooring removal, slab and wall drying, readings and photographs
- Licensed contractor: new flooring, baseboard, drywall, texture, paint and cabinet repair
How do the plumber's visit and the drying fit together?
They overlap on purpose. A crew can shut the water, extract what is on the floor and set equipment while the plumber schedules detection, so the slab is not sitting wet for another two days. The crew then returns after the repair opening is closed, because the patch itself puts fresh water into the concrete.
Order the calls to suit whichever is slower. If a plumber cannot get there until tomorrow, drying should start today; if the plumber is on the way, the crew can plan around the concrete work rather than set equipment twice.
Expect dust and noise for part of a day if concrete has to come out, and a patch in the floor afterward. A re-route instead abandons the buried section and runs a new line through a wall or the attic, trading slab work for drywall work.
The one deadline nobody should negotiate is new flooring. A slab gives up moisture slowly and mostly through its surface, and planks laid over concrete that is still releasing it will cup, lift or trap that moisture underneath. Wait for the reading, not the calendar.
What catches the next one early?
A habit and a working valve. Read your meter once a month with the house quiet, open the water bill rather than paying it on autopilot, and confirm the main shut-off actually turns before you need it. For a house that sits empty in summer, arrange a walk-through inside, not a look from the curb.
The monthly meter check takes two minutes and finds leaks while they are still cheap. A reading noted on a phone each month turns the water bill into a trend, and a trend is what a slab leak looks like long before a floor feels warm.
Seasonal absence is the local multiplier. Many Valley homeowners leave for the summer, and a leak in an empty house runs for weeks in rooms nobody enters, which is how a pinhole becomes wet drywall, swollen cabinets and a mold question.
If you do find a warm spot or a moving meter, photograph the floor and the meter face before anything moves and call early. Documentation costs nothing at the start and cannot be recreated later; slab leak cleanup covers what happens from there, and phones are answered 24/7 at (833) 490-5225.
Frequently asked questions
Can a slab leak drain away without ever wetting my floor?
Yes, and that is common on a cold-water line. Water can follow the soil or run out past the stem wall without surfacing indoors, so the bill and the meter are the only evidence for months. A meter test with the house shut off tells you whether water is leaving the system at all.
Does the entire floor have to come up?
Usually not. A plumber opens only the area needed for the repair, or avoids the concrete altogether with a re-route. The crew removes flooring where readings say the material underneath cannot dry through it, which is often part of one or two rooms rather than a whole house.
Will a water softener prevent the next slab leak?
It may reduce scale in heaters, fittings and fixtures, which is why many Valley homeowners have one. Nobody can honestly promise it saves a buried line that has already carried very hard water for decades, and no softener addresses soil movement or a joint that was marginal from the start.
How many drying days should I expect for a wet slab?
Plan on several days for a single room and longer where the leak ran for a while, because concrete releases moisture slowly and only from the surface. Monsoon weeks stretch it further, since the dehumidifier fights a higher outdoor dew point as well as the floor.
Should I repipe the whole house after one leak?
That is a plumber's judgement, based on pipe condition, water pressure and whether this is the first failure. Plenty of local homeowners repair the first leak and re-route after a second one. It is not restoration work, and it is not a decision to make while the floor is still wet.
Sources
- City of Phoenix Water Services - water quality reports and plumbing guidance
- Arizona Registrar of Contractors - contractor licensing and licence lookup
- IICRC - the ANSI/IICRC S500 standard, including specialty drying of dense materials
- U.S. EPA - Mold and moisture guidance
This guide is general information for Maricopa County homeowners, not a substitute for an on-site inspection. Prices are estimates. See our disclaimer.