What a slab leak is
Most houses in the Phoenix Valley sit on a concrete slab poured directly on the ground. The University of Arizona Cooperative Extension lists floating and monolithic slabs as the most common foundation types in Arizona. In many of these homes, water lines run under or through the slab. When one of them starts leaking, the water spreads under the flooring and into the bottoms of walls, often without a visible puddle.
A slab leak is really two problems:
- The leak itself. Finding and fixing a pipe under concrete is plumbing work. A plumber or leak detection specialist locates the leak, then either repairs it through the floor or reroutes the line through the walls or attic.
- The water damage it caused. Wet flooring, carpet pad, baseboards, drywall and cabinets need to be dried or removed. That’s the part a water damage restoration provider handles.
This page is about the second part. If nobody has confirmed or repaired the leak yet, call a plumber first, or at the same time. Drying a floor while the pipe underneath is still leaking won’t get anywhere.
Signs of a leak under the slab
Slab leaks are easy to miss because the water is hidden. Watch for:
- A warm spot on the floor. The Smart Home Water Guide, published with the City of Phoenix and the Arizona Municipal Water Users Association, suggests feeling for “hot spots” on the floor after running hot water nearby. A warm patch can mean a leaking hot water line under the concrete.
- Damp flooring with no obvious source. Carpet that feels wet along one wall, grout lines that stay dark, or laminate and wood that start to cup or lift.
- Swollen baseboards or stains at the bottom of drywall, especially along an interior wall.
- Water use that climbs for no reason. The City of Phoenix notes that month-to-month increases in water use you can’t explain may indicate a leak.
None of these proves a slab leak on its own. Toilets, irrigation valves, water softeners, pool autofills and evaporative coolers can all keep a water meter turning, so rule those out too.
Check the water meter first
The water meter is the simplest home test. The Smart Home Water Guide describes the steps:
- Turn off everything that uses water: faucets, toilets, irrigation, the pool autofill, the softener and the evaporative cooler, if you have one.
- Find the meter. Most residential meters sit in a concrete box near the curb or sidewalk at the front of the property.
- Watch the dial. On analog meters, look at the sweep hand and the small low-flow indicator (a triangle, star or gear). If either moves, water is flowing somewhere. For slow leaks, take two readings 20 minutes apart. On digital meters, watch the flow rate display.
- Now close your home’s main shut-off valve. If the meter still moves, the leak is in the service line between the meter and the house. If it stops, the leak is inside the house’s plumbing, which includes lines under the slab.
Don’t turn the valve inside the meter box. The City of Phoenix asks residents not to: it takes a special tool, and you may be charged for damage to the meter. If your home’s valve is stuck or broken, call your city’s water department and ask them to shut off service at the meter.
What to do while you wait for help
- Shut off the water at the main valve if you’ve confirmed a leak and can’t isolate it. In Phoenix, that valve is usually at the front of the house near a hose bib, where a pipe comes out of the ground and into the wall. Some older homes have it at the back. Our shut-off valve guide has more detail.
- Take photos and video of damp flooring, stained baseboards and the meter readings. Keep your recent water bills. Your insurance company may ask for all of it.
- Move furniture, rugs and boxes off wet flooring.
- Schedule the leak repair with a plumber or leak detection specialist.
- Start the drying process as soon as the source is under control. Waiting gives mold time to start.
What slab leak water damage cleanup involves
Every job is different, but the work usually follows the same pattern.
Moisture mapping. The provider uses moisture meters, and often a thermal camera, to find how far the water spread under the flooring and up into the walls. Water from a slab leak tends to travel sideways, so the wet area is often larger than the spot where you first noticed it.
Removing what can’t be dried. Soaked carpet pad, swollen baseboards, laminate and particleboard cabinet bases usually come out. The provider may cut the bottom of the drywall so the wall cavity can dry. Tile and other hard flooring can sometimes stay if the readings allow it.
Coordinating with the plumbing repair. If the plumber opens the floor to reach the pipe, that area has to be repaired later anyway. If the line is rerouted through the walls or attic, there will be drywall openings to plan around. Tell both parties who is doing what, and in what order.
Drying. Air movers and dehumidifiers run until the materials reach their dry targets. Concrete holds moisture longer than drywall does, and flooring shouldn’t go back down over a slab that’s still wet. The provider should record readings each day.
Checking for mold. A slow leak may have been going on for weeks. Backs of baseboards, the underside of carpet pad and the bottoms of cabinets are the first places to look.
Putting things back. Some providers also replace flooring, drywall and baseboards. Others only handle the water removal and drying. Ask which one you’re talking to.
Phoenix Valley details that matter
- Hard water. The City of Phoenix’s 2025 water quality report lists total hardness of 10 to 17.6 grains per gallon and notes that hard water can cause scaling in pipes, water heaters and fixtures.
- Your side of the meter. Phoenix Water Services repairs leaks on the street side of the meter. Leaks on private property are the owner’s responsibility.
- Lots of things use water automatically. Pools, irrigation systems, softeners and evaporative coolers are common in Valley homes, and any of them can make the meter move. That’s why the shut-off test above matters before anyone starts breaking concrete.
Questions to ask a restoration provider
- Will you share moisture readings and photos so I can give them to my insurer?
- Which materials do you expect to remove, and why?
- How will you coordinate with my plumber?
- Do you handle the rebuild, or only the water removal and drying?
- What is your Arizona contractor license number, and can you send proof of insurance?