If your home sits on a concrete slab — as most homes across the Sun Belt do, from Texas and Florida to Arizona and Southern California — your water and sewer lines run under that slab. A leak down there is called a slab leak, and it is one of the more expensive plumbing problems a homeowner can face. Here is how to tell if you have one, how pros find it, and what the repairs actually involve.
Real warning signs
- A hot spot on the floor. A hot-water line leaking under the slab warms the concrete above it. If one section of tile or flooring feels noticeably warm underfoot, pay attention.
- The sound of running water when every fixture is off. Put your ear to the floor in a quiet house — a slab leak often produces a faint hissing or rushing sound.
- A water bill that jumps with no change in usage. Compare several months; a steady climb points to a continuous leak.
- Low water pressure throughout the house, or a single fixture that lost pressure while the rest are fine.
- Damp spots, mildew, or a musty smell near the base of walls, especially on ground-floor exterior walls.
- Cracks in the slab or flooring that appear alongside any of the above — water erodes the soil beneath the concrete.
The two-minute meter test
Before calling anyone, confirm you actually have a leak. Turn off every water-using fixture and appliance in the house — including ice makers and irrigation — then check your water meter. Most meters have a small leak indicator (a triangle or star-shaped dial). If it is moving with everything off, water is escaping somewhere. Note the meter reading, wait 30–60 minutes without using any water, and read it again. A change confirms a leak. This test does not tell you where the leak is, only that one exists.
What actually causes slab leaks
Honest causes, no exaggeration:
- Expansive soil. Clay-heavy soils common in Texas and the Southwest swell when wet and shrink when dry, shifting the slab and stressing the pipes beneath it. This is the leading cause in much of the Sun Belt.
- Abrasion. Pipes expand and contract with temperature changes, rubbing against concrete, gravel, or rebar until the metal wears through — copper lines are especially vulnerable.
- Corrosion. Aggressive water chemistry or contact between dissimilar metals eats through pipe walls over decades.
- Poor installation. Kinked lines, inadequate sleeving where pipes pass through concrete, or joints stressed during the original pour fail early.
What does not cause slab leaks in any meaningful sense: earthquakes (outside genuine seismic zones), and hard water itself. One correction worth making explicitly — hard water is not acidic. Its pH typically runs around 7 to 8.5, slightly alkaline. Claims of pH 1 to 4 describe battery acid, not tap water.
How professionals locate the leak
Finding the leak without tearing up the whole floor is a specialty called leak detection, and it matters — accurate location is the difference between one hole in your slab and five. Methods include:
- Acoustic listening equipment that pinpoints the hiss of pressurized water escaping.
- Thermal imaging cameras that reveal the warm plume from a hot-water leak.
- Pressure testing of individual lines to isolate which run is losing pressure.
- Video inspection for sewer-side leaks under the slab.
Professional leak detection typically costs $300–$800 nationally. Be wary of anyone who wants to start jackhammering before they have located the leak precisely.
Repair options and what they cost
There is no single “slab leak repair” — the right method depends on the pipe’s age, condition, and how many leaks have already occurred:
- Spot repair. Open the slab at the leak location and repair or replace that section of pipe. Cheapest when the rest of the system is sound: typically $500–$2,000 nationally, plus flooring restoration.
- Reroute (overhead repipe). Abandon the leaking under-slab line entirely and run a new line through walls or the attic. The most common recommendation for older systems with recurring leaks: typically $1,500–$5,000+ nationally depending on the number of lines and the home’s layout.
- Tunneling. Digging beneath the slab from outside to access the pipe without breaking interior flooring. Useful when flooring is expensive to replace; labor-intensive and typically $3,000–$6,000+ nationally.
- Epoxy pipe lining. Coating the inside of the existing pipe with epoxy. Less invasive, but controversial for potable water lines and not appropriate for every situation — get a second opinion before agreeing to it.
If your home has had two or more slab leaks, most plumbers will recommend a full reroute rather than another spot repair — the system is telling you it is at the end of its life. Also check your homeowner’s insurance: many policies cover the access (breaking and restoring the slab) even when they exclude the pipe repair itself.
Do not ignore it
A slab leak does not fix itself and does not stay small. Ongoing water under the slab erodes soil, undermines the foundation, feeds mold, and — with a hot-water leak — runs your water heater nonstop. If the meter test confirms a leak, get detection scheduled within days, not months.
Get a free quote — America’s Service Plumber is a free matching service. Tell us what you need and we will connect you with licensed local plumbers in your area for free quotes on leak detection and slab leak repair.
