6 signs you have a slab leak in your Phoenix home

A slab leak is a leak in a water or drain line that runs under or inside a concrete foundation slab. Many Phoenix-area homes are built slab on grade, with supply lines running under the floor, so a pinhole in one of those pipes can leak for weeks before it shows. HomeGuide's slab leak repair guide lists the usual causes: corroded metal pipe, stress on the pipe from excessive heat or pressure, weak points in plastic or PEX pipe, and damage from hard or acidic water. Hard water is a constant here; see our hard water guide.

HomeGuide lists six signs. Here is what each looks like in practice:

1. A warm spot on the floor. A leak in a hot water line under the slab warms the concrete above it. Walk barefoot over tile or check with the back of your hand, especially near the water heater, kitchen and bathrooms.
2. A sudden jump in your water bill. Compare the same month last year. A rise with no change in habits or landscaping is a reason to test the meter.
3. The sound of running water when everything is off. Listen near floors and lower walls at night when the house is quiet.
4. A sudden change in water pressure. Water escaping under the slab can lower pressure at fixtures.
5. Water or damp flooring. Damp carpet, lifting laminate, a musty smell or mildew along baseboards with no plumbing fixture nearby.
6. New cracks in the foundation or floor. Water moving under the slab can wash out or swell the soil beneath it.

One sign alone is not proof. A water heater can make the floor near it warm, and a running toilet can raise a bill. Two or more signs together is the time to test.

The EPA's WaterSense Fix a Leak Week page gives a simple meter test: check your water meter before and after a two-hour period when no water is being used. If the meter changes at all, you probably have a leak. Before you start, turn off irrigation, the ice maker and any softener regeneration cycle.

Then narrow it down. The EPA suggests putting a few drops of food coloring in each toilet tank; if color shows up in the bowl after 10 minutes, the flapper is leaking. If every toilet passes and the meter still moves with all fixtures off, the leak is somewhere in the supply piping, which in a slab home often means under the floor. If you have a whole-house shut-off valve, closing it and watching the meter can also tell you whether the leak is between the meter and the house (the yard line) or inside.

The EPA says the average household's leaks can waste more than 9,300 gallons a year. A slab leak can waste far more, and keeps soaking the soil under the house the whole time.

• If water is coming up through the floor or the meter is spinning fast, close the main shut-off valve. Our emergency guide explains how to find it.
• If the leak looks like it is on the city side of the meter or in the street, call your water utility. Phoenix's Water Services FAQ lists 602-261-8000 for reporting a water emergency.
• Photograph damp areas, cracks and your recent bills. Your insurer may ask for them.
• Call a licensed plumber to locate the leak before anyone breaks concrete.

A plumber first isolates which line is leaking, usually with pressure tests on the hot and cold sides, then pinpoints the location with acoustic or other detection equipment. Ask how the leak was located and get the result in writing; you should not pay for concrete demolition based on a guess. Our leak detection guide covers the process.

HomeGuide's national ranges for the common repair methods:

HomeGuide also puts a foundation inspection at $300 to $750 if you cannot find the source yourself. These are national figures; get written local quotes. Our Phoenix cost guide has more ranges.

Slab repairs often cost well over $1,000, and Arizona's handyman exemption in A.R.S. 32-1121 only covers casual or minor jobs under $1,000 that need no building permit, so hire a licensed contractor. Confirm the company's license with the Arizona Registrar of Contractors and read our hiring guide. If two contractors recommend different methods, ask each to explain why.

We are an independent guide, not a contractor; we do not perform leak detection or repairs. To reach a plumber, call one of the licensed contractors listed on this page or see all listed contractors. Questions about this guide: email us. We do not take service requests.