A slab leak almost never starts with a flood. It starts with a water bill that is a little higher than last year, a floor tile that feels warm under bare feet, or a hiss you only hear at night. By the time water shows up on the surface, it has usually been running for weeks.
This guide covers how to check for one yourself, what the signs mean, and when it is time to call for professional leak detection.
Why slab leaks are common in Temecula
Three facts about Temecula housing explain most of it:
- Age. The median Temecula home was built in 1998, and about 80% were built between 1980 and 2009, according to Census ACS data. Most of those homes have copper supply lines buried under a concrete slab.
- Hard water. Rancho California Water District's 2021 water quality report shows imported water averaging 268 mg/L of hardness, about 15.7 grains per gallon. The USGS classifies anything above 180 mg/L as very hard.
- Pressure. Hillside neighborhoods like Redhawk often have street pressure above 80 psi, the point at which the California Plumbing Code requires a pressure reducing valve.
Copper that is 25 to 45 years old, carrying very hard water at high pressure, eventually pinholes. Hot water lines usually go first.
The water meter test (do this first)
Your meter is in a concrete box near the curb. Lift the lid and find the low-flow indicator, a small triangle, star or dial that spins with even a trickle of flow.
- Turn off every faucet, shower, the dishwasher, washer and ice maker.
- Turn off the irrigation controller.
- Watch the low-flow indicator for 15 minutes. Take a photo at the start and end.
- If it moved, close your house shutoff valve (usually near the front hose bib or in the garage) and watch again.
If the meter stops when the house valve is closed, the leak is inside the house. If it keeps moving, the leak is in the yard line or irrigation. A running toilet will also move the meter, so do a dye test in each tank first.
Signs that point to a slab leak specifically
- A warm or hot spot on the floor, often near a bathroom or kitchen. That is a hot water line.
- The sound of running water with everything off.
- Damp carpet or cupped wood flooring with no plumbing fixture nearby.
- Water heater running more than usual. If hot water is leaking under the slab, the heater keeps refilling and reheating.
- Cracks in tile or slab that appear along with moisture. Cracks alone are not proof.
Isolate hot from cold
If you suspect the hot side, close the cold water inlet valve on top of your water heater and watch the meter again. If the meter stops, the leak is on the hot side. That one check saves time during professional detection.
What professional detection adds
A plumber narrows the leak to a small area using acoustic ground microphones, which pick up the hiss of pressurized water through concrete, plus a thermal camera for hot-side leaks and moisture meters. The goal is to open the smallest possible area, or to avoid opening the slab at all by rerouting the line. Detection usually costs $150 to $600, based on published 2026 data.
Mistakes that make it worse
- Waiting for it to dry out. A pressurized leak does not stop on its own.
- Breaking concrete on a guess. Without detection you may open the wrong spot.
- Ignoring the PRV. If pressure is over 80 psi, fix that too or the next leak will follow.
Repair options in one paragraph
Once found, a slab leak can be fixed with a spot repair through the slab, a reroute through the attic and walls, or a whole-house repipe. One leak in an otherwise healthy system usually gets a spot repair or reroute. Repeat leaks usually justify a repipe. Our slab leak repair page compares them with current cost ranges.