Most Hollister homes on slab foundations have supply lines routed through or under the concrete, which is why this is a local problem rather than an exotic one.
The Signs
- A water bill that jumped with no change in household habits. Frequently the first clue.
- The sound of running water when every fixture is off, often heard best at night.
- A warm or hot patch on the floor, which indicates the hot water line. Cold line leaks give no temperature clue, which is why they run longer.
- Damp carpet, buckling flooring or damp baseboards with no source above.
- Reduced water pressure throughout the house.
- Cracks appearing in flooring or walls as the soil beneath moves.
- A musty smell, or mould appearing at the base of walls.
Any one of these on its own has other explanations. Two or three together is worth acting on.
The Meter Test
The quickest confirmation, and you can do it yourself.
Turn off every water-using fixture and appliance in the house, including the ice maker and any irrigation. Then look at the water meter. Most meters have a small triangular or star-shaped low-flow indicator that turns when even a trickle is moving.
If it is turning with everything off, water is escaping somewhere. That does not prove the leak is under the slab, but it proves there is one. Mark the meter reading, wait an hour without using water, and check again for a second confirmation.
Why Waiting Is Expensive
This is not a dripping tap. Water escaping under a foundation goes somewhere, and where it goes matters.
It saturates and erodes the soil supporting the concrete, which is what produces the floor cracks and, eventually, movement in the structure itself. It damages flooring and framing from below. It runs continuously on your bill. And in a region where soil movement is already a factor, adding saturation beneath a foundation is not a small thing.
The repair cost generally rises the longer it runs, because the scope shifts from a pipe to a pipe plus everything the water affected.
Locating It
Detection equipment does the work: acoustic listening gear to hear the escape through the concrete, pressure testing to confirm which line is involved and isolate the section, and sometimes thermal imaging for hot water lines.
The point of locating it properly is to avoid opening concrete speculatively. A leak found to within a small area means one targeted access point rather than exploratory demolition.
The Repair Options
Spot repair. Open the slab at the located point, repair the section, close it. Appropriate when the leak is isolated and the rest of the plumbing is sound. The most disruptive in the short term, the least expensive when it fits.
Reroute. Abandon the failed line under the slab and run a new one overhead through walls and attic space. Common when the same line has leaked before, or where the slab access point is somewhere awkward such as beneath a kitchen island.
Repipe. Where the pipe has failed in multiple places or the system is at the end of its life, replacing the supply lines throughout takes them out of the concrete entirely and ends the recurring problem. This is the permanent answer for a house with a history of slab leaks.
Chasing successive slab leaks in aging pipe tends to be expensive and temporary, which is why the conversation often widens after the second one.
Why Pipes Under Slabs Fail Here
Several factors, usually in combination. Age and the material used when the house was built. Soil chemistry acting on the outside of the pipe. Abrasion where a pipe rubs against concrete as the ground moves, which in an area with active ground movement is not theoretical. High water pressure accelerating wear on everything. And mineral content in local groundwater working on the inside, as covered in our post on protecting your plumbing from hard water.
What to Do Now
If you suspect one, run the meter test. If the meter is moving, know where your main shut-off valve is and make sure it works, because that is what limits the damage if the leak worsens suddenly.
Then get it located before anything is opened up. And contact your insurer early: many policies cover the resulting water damage and the access work while excluding the pipe itself, and the distinction is worth understanding before work starts.
Talk to a Licensed Plumber
DAE Plumbing handles underground plumbing repair and leak location across Hollister and San Benito County. Call (831) 801-1079 or use the contact page.