Slab Leak or Foundation Problem? How to Tell, Who to Call

Your water meter can tell you a lot in a few minutes. A Texas river authority's guide to its meters describes the method:

1. Turn off all water inside and outside the house, so nothing is using any.
2. Find the meter box. In Denton, it's usually in the front yard, under a round metal lid.
3. Look for flow. With everything off, the meter's flow reading should be zero. If it shows flow, a leak is likely somewhere.

The same guide adds that if your own meter reading is far above what your bill shows, it's worth checking for a leak. The meter test won't say where the water is going. It could be a running toilet, a line in the yard or a pipe under the slab. It just tells you whether to call a plumber.

The City of Denton draws the line at the meter box. A leak between the street and the meter box is the city's responsibility, and you report it at (940) 349-7000. A leak between the meter box and your drain is the homeowner's, and the city's advice is to call a certified plumber as soon as possible.

Fixing that leak is plumbing work, and Texas requires a licensed plumber for it, with one exception: a property owner may do plumbing in their own homestead. In Flower Mound, water and sewer line repairs also need a permit, and the plumber must be licensed by the state and registered with the town. Other towns set their own rules, so ask yours.

In 2005, a Houston investigative plumber described his company's method to the Foundation Performance Association, a Houston group of engineers and repair firms. He said there were no published standards for testing plumbing under a house, so leak detection companies had developed their own. His steps were:

1. A hydrostatic test. The toilets are pulled, the drain lines under the slab are filled with water, and the level is watched for 30 minutes.
2. A camera. If the lines don't hold water, a video camera goes into the line to look for the likely leak.
3. Test balls. Inflatable balls block off sections of pipe, which are refilled one by one until the leak is found.
4. A flow test, if needed, to see how much water is lost in normal use.

He also cautioned that a flow test right after a hydrostatic test may not be accurate, because the voids around a leaking pipe will already be full of water. That detail shows why a leak matters to a foundation: the water goes somewhere, and under a slab that somewhere is the soil.

Ask for the results in writing. A Foundation Performance Association repair guideline has the contractor provide a written report of the leak test done after a pier repair.

Pipe age matters

The same talk gave a feel for how long drain pipes last. He said cast iron usually lasts 35 to 50 years, though he had seen it fail in as little as 20. He called the ABS plastic pipe used from 1970 to 1975 "not so good," and said PVC, used since 1975, was performing much better. That was one plumber's experience in Houston, not a rule, but if your house is from the 1960s or 1970s it's a fair question to ask a plumber.

The two trades meet again whenever a house is lifted. Any repair that jacks or lifts the house should include a leak test on the water and sewer lines, the Texas engineers' guidelines say. Leaks the test turns up should be fixed. An engineer's full investigation can include a plumbing test too.

Some repair companies build that test into their price. One company with a Lewisville office says its average repair cost includes a hydrostatic plumbing test by an outside plumber. When you compare quotes, it's worth asking whether a before-and-after leak test is included. Our cost guide covers what else to look for.

There's no single rule, but these patterns are a reasonable guide:

• The meter shows flow with everything off. Call a licensed plumber first. If the leak is on the street side of the meter in Denton, call the city.
• The meter is still, and cracks are growing or floors slope. Start with a foundation inspection, which measures the floors.
• Both are happening. You'll likely need both. Fixing a leak first stops the water. A floor survey then shows whether the slab has moved and needs more.

If you're on the sandy middle band of Denton County, where the soil moves less, water deserves an extra-hard look whenever a crack keeps growing. Our soil and rock guide shows which band you're on.