Slab Leak Warning Signs

The most common signs of a slab leak are an unexplained high water bill, a warm or hot spot on the floor, the sound of running water when every fixture is off, and a drop in water pressure. If you notice one or more, check your water meter and have a plumber confirm the leak with proper detection equipment before any repair begins.

A slab leak happens when a water line under your home’s concrete foundation starts to leak. Left alone, it can raise your water bill, damage flooring and put pressure on the slab itself.

Common Signs of a Slab Leak

A slab leak rarely announces itself the way a burst pipe does. Instead, it usually shows up as one or more small, easy-to-miss changes around the house:

• Unexplained high water bill. Usage habits haven’t changed, but the bill jumps from one cycle to the next.
• Hot spot on the floor. A patch of tile, vinyl or thin carpet feels warm underfoot with no heating system beneath it — usually a leaking hot water line.
• Sound of running water. A faint hiss or trickle from the floor or a wall, most noticeable when the house is quiet.
• Low water pressure. Pressure drops throughout the house, or at one fixture, because water is escaping before it reaches the tap.
• Damp carpet, baseboards or flooring. A damp area or musty smell with no obvious source nearby.
• Cracks in flooring or the foundation. Separating grout lines, cracked flooring, or hairline cracks in the slab or a nearby wall.
• Standing water or mold odor in a slab-on-grade home with no other plumbing explanation.

Any single sign can have another cause — a running toilet, an irrigation leak, seasonal humidity. Two or more together are worth checking further.

Check the Water Meter

A water meter leak test is a simple way to find out whether water is flowing somewhere in your system, even when everything appears to be off.

1. 1Find your water meter — typically in a meter box near the curb, sidewalk or property line.
2. 2Turn off every water-using fixture and appliance inside and outside — no dishwasher, no washing machine, no irrigation, and confirm toilets aren’t mid-refill.
3. 3Read the meter — most have a small leak indicator (a triangle or dial) that turns when water passes through, plus a digital or dial read-out.
4. 4Wait 15–30 minutes without using any water.
5. 5Check the meter again — if the leak indicator has moved, or the usage number changed, water is moving through the system somewhere.

A positive result confirms a leak exists between the meter and your home’s fixtures — it doesn’t by itself confirm the leak is under the slab; it could be an irrigation line, a toilet flapper, or a leak elsewhere in the yard. In most of Moreno Valley, Eastern Municipal Water District (EMWD) provides water service, though the exact provider can vary by address.

Hot Floors, Damp Areas and Running-Water Sounds

These three signs are worth looking at together because they often point to the same underlying issue: a leaking hot water line under the slab.

Hot floors. Hot water lines usually run closer to the slab surface than cold lines. A pinhole leak lets hot water seep into the surrounding concrete and soil, and that heat transfers upward.

Damp or discolored areas. Moisture pushing up through a slab can show as a damp patch of carpet, a warped section of laminate or vinyl, baseboard staining, or a musty smell. Concrete and soil absorb moisture before it’s visible, so by the time you notice dampness, the leak has often been active a while.

Running-water sounds. With appliances off and the house quiet, a leak under the slab can sometimes be heard as a faint hiss or trickle near the leak’s location.

Why Under-Slab Pipes Leak

• Corrosion. Metal pipes can corrode from the inside (mineral content) or the outside (soil and moisture contact), thinning the pipe wall until it fails.
• Ground movement. Soil shifting beneath a slab — from moisture changes, settling or seismic activity — can stress a pipe joint or bend.
• Water pressure. Consistently high pressure adds ongoing stress to joints and fittings, which can accelerate a developing failure.
• Poor installation or pipe defects. A poorly sealed fitting or a manufacturing flaw can leak years after installation.
• Age. Older pipe materials are more likely to leak as they near the end of their service life, depending on material and usage.

We don’t have a verified, sourced basis for which Moreno Valley neighborhoods have older or newer plumbing, so this guide makes no such claim — your home’s age and original pipe material are useful details to share with your plumber.

How Professionals Confirm the Leak

Because a slab leak is hidden under concrete, confirming its exact location before any demolition keeps the repair focused instead of guesswork. Plumbers typically combine a few methods:

• Acoustic leak detection. Sensitive listening equipment picks up escaping water under pressure as the plumber moves across the floor to find where the sound is loudest.
• Thermal imaging. A thermal camera reads surface temperature differences; hot water line leaks often warm the surrounding slab.
• Pressure testing. Isolating sections of the line and testing pressure helps confirm a leak’s presence and rule out other causes.
• Visual and moisture inspection. Cracked flooring, foundation moisture and efflorescence support the acoustic and thermal findings.

Combining methods generally gives a more accurate result than relying on just one, which affects how much of the slab needs to be opened for repair.

Repair Options After Detection

Once a slab leak is located and confirmed, there are generally three approaches, and the right one depends on the leak’s location, the plumbing system’s age and condition, and how accessible the area is.

• Spot repair. The slab is opened directly above the leak, the damaged pipe section is repaired or replaced, and the concrete is patched — often the most direct option for a single, isolated leak.
• Reroute. A new line is run around the leak — often through the attic or walls — bypassing the damaged section entirely.
• Whole-house repiping. If the pipe material shows a pattern of repeated leaks or the system is nearing end of service life, replacing the home’s water lines addresses the underlying cause.

Permits are issued by the City’s Building & Safety Division through its SimpliCITY portal. See slab leak repair and leak detection.

How Urgent Is a Slab Leak?

• Constant running water, a fast-climbing bill, or visible standing water — treat this as time-sensitive.
• A steady hot spot with a rising bill but no visible water — worth scheduling promptly, since a hot water line leak wastes water and energy the whole time it’s active.
• A single small warm spot with a stable water bill — still worth having checked, though it may not require an immediate response.

A slab leak generally gets worse, not better, the longer it runs. Confirming what you’re dealing with early gives you more repair options and less secondary damage to address.

Slab Leak FAQs