Signs of a Slab Leak in a Phoenix Home

Why slab leaks come up so often in the Valley

Most houses across metro Phoenix sit on concrete slab-on-grade foundations, and in many of them the water supply lines run under or inside that slab. In the City of Phoenix the median home was built around 1984, according to ACS-based figures on city-data.com, so a lot of under-slab pipe has been in service for decades. This Old House lists age, water chemistry and shifting soil among the reasons pipes deteriorate, along with corrosion and pressure problems. Hard water, which the City lists at 10 to 17.6 grains per gallon, is part of that chemistry; our guide to hard water in Phoenix covers how it affects plumbing.

A slab leak is usually a pressurized supply line, hot or cold. Drain lines under the slab can leak too, but they behave differently: they only leak when water is running down them, and they rarely show up on the meter. That difference shapes how you look for each one. A supply leak runs all day and night whether anyone is home, so it tends to show up in the bill and on the meter first. A drain leak is quieter and slower, and is more often found by smell, by a slow drain, or with a camera run through the line.

Early signs you can notice

A water bill that rises for no reason

Valley water use swings with the seasons because of landscape watering, so compare a bill to the same month last year, not to last month. A jump with no change in irrigation, guests or a pool fill is worth checking. EPA's WaterSense program says one in ten homes has leaks that waste 90 gallons or more a day, which is enough to show up clearly on a bill.

Running water you cannot account for

With the house quiet, listen near floors and lower walls. A faint hiss or trickle when nothing is on can be water escaping under pressure. Rule out a toilet first; a worn flapper is far more common than a slab leak.

A warm spot on the floor

A leak on a hot water line warms the concrete around it. Bare feet on tile often find it first. In Phoenix summers, rule out sun through a window or a duct above, but a warm patch in a shaded hallway or closet is a strong clue. A related sign is a water heater that seems to run constantly or never quite keeps up, because it is reheating water that is leaving through the floor.

Dropping pressure

This Old House lists minor drops in water pressure among the early signs. A leak large enough to lower pressure at fixtures is usually also obvious on the meter. Our low water pressure guide covers the many other causes worth ruling out.

Later signs that mean it has been going on a while

• Damp or discolored carpet, swollen baseboards or wood flooring that cups or buckles
• Mold or a musty smell in one room with no visible source
• Cracks in tile or the slab that keep widening
• Persistent moisture or soggy soil along the outside of the foundation

These later signs matter for more than repair. Country Financial notes that slab leaks that go undetected for months can be classified as gradual damage and denied by insurers, so acting early protects your claim as well as your floors.

Confirm it yourself: the two-hour meter test

EPA's WaterSense guidance is simple: read the meter, use no water for two hours, and read it again. If the reading changed, you probably have a leak. To do it well:

1. Turn off irrigation timers, the ice maker, the softener (or put it in bypass so it cannot regenerate), and any evaporative cooler or pool fill.
2. Make sure no toilets are running and nobody will use water.
3. Find the meter box, usually near the street, and lift the lid carefully. Desert meter boxes can hold insects or other surprises, so look before you reach in, and do not try to operate the valve inside it.
4. Note the reading or take a photo, wait two hours, and check again.

If the meter moved, close the main shut-off at the house and watch the meter again. If it stops, the leak is inside the house or under the slab. If it keeps moving, the leak is probably in the buried line between the meter and the house, which is a yard water line repair rather than a slab job. In Phoenix, the City handles leaks on its side of the meter, and property owners are responsible for the lines on their side.

To tell hot from cold, close the cold supply valve on top of the water heater and repeat the check. If the meter stops, the leak is on the hot side, which fits with a warm floor.

What a leak detection visit involves

Professional leak detection in Phoenix usually starts by isolating hot and cold lines and pressure-testing them to confirm which one is losing water. The technician then uses listening equipment and sometimes thermal imaging to narrow the leak to a small area of floor. HomeAdvisor's 2025 data puts leak detection at about $150 to $400, with an average near $280. This Old House lists slab leak detection at $150 to $600. Accurate location is what keeps the repair from turning into a hunt through your floors.

Repair options and what they cost

HomeAdvisor puts the overall national average for slab leak repair at about $2,280, with most jobs between $630 and $4,400. Direct access makes sense for a single leak in an easy spot. If a home has had more than one slab leak, a reroute or whole-house repipe often costs less over time than opening the floor again next year. A plumber offering slab leak repair in Phoenix should explain why they recommend one option over another. For broader pricing context, see what plumbing work costs in Phoenix.

What about insurance?

Country Financial explains that many policies may cover the cost of tearing out and replacing the section of slab needed to reach a pipe after a sudden failure, plus restoring floors, but most do not pay to fix the pipe itself. Some policies cap foundation-related repairs, and some need a service line endorsement. Call your insurer before the floor is opened and ask what they will need to see.

What to do today if you suspect one

• Run the meter test above, and close the main valve if the leak looks large.
• If the leak is on the hot side, turn the water heater off until it is repaired.
• Photograph any damp floors, swollen trim or warm spots.
• If water is actively spreading, follow our burst pipe first steps.
• Book detection before any demolition. Owners in Gilbert and Tempe face the same slab-on-grade setup, and the same order of steps applies.

If you are buying an older house, a plumbing inspection with a meter test is a quick way to find out whether a slab leak is already running before you close.