Quick Answer
Ironclad Plumbing publishes this guide because catching a slab leak early is the difference between a $2,000 repair and a $15,000+ foundation problem, and most Austin homeowners don’t know the warning signs. A slab leak is a leak in the water pipes running beneath your home’s concrete foundation. You can’t see the pipe. You often can’t see the leak. But there are clear warning signs, and catching a slab leak early is the difference between a $2,000 repair and a $15,000+ foundation problem.
| Warning Sign | What It Looks Like | How Urgent |
|---|---|---|
| Unexplained spike in water bill | Usage jumped 30-50%+ with no change in behavior | Investigate this week |
| Sound of running water when nothing is on | Faint hissing or rushing sound near the floor or walls | Investigate this week |
| Warm or hot spot on the floor | One area of tile or concrete floor feels noticeably warmer than surrounding areas | Investigate ASAP (hot water line leak) |
| Damp carpet or flooring | Moisture or dampness in carpet, warping in wood/laminate, with no visible source above | Investigate ASAP |
| Cracks in walls or foundation | New or widening cracks in interior walls, especially near the base, or visible cracks in exterior foundation | Investigate ASAP |
| Mold or mildew smell | Musty smell near the floor, especially in rooms that shouldn’t be damp | Investigate this week |
| Low water pressure | Gradual decline in pressure throughout the house (not just one fixture) | Investigate this week |
| Water meter spinning when nothing is on | All fixtures off, nobody using water, but the meter’s flow indicator is moving | Investigate today |
| Foundation shifting or doors sticking | Doors that used to close fine now stick or won’t latch. Floors feel uneven. | Investigate ASAP |
If you have 2 or more of these signs at the same time, call for leak detection. Don’t wait.
Why Slab Leaks Are an Austin Problem
Austin sits on a mix of clay soil and limestone bedrock. Clay soil expands when wet and contracts when dry. This seasonal expansion and contraction puts continuous stress on the pipes running through and under your foundation. Add Austin’s very hard water (15-25 GPG), which corrodes copper pipe from the inside over years, and you have two forces working against your under-slab piping at all times.
Homes built before the mid-1990s with original copper supply lines under the slab are the most common candidates for slab leaks. The combination of age, hard water corrosion, soil movement, and decades of thermal expansion/contraction eventually creates pinhole leaks or joint failures.
Newer homes with PEX piping under the slab are significantly less prone to slab leaks because PEX is flexible (accommodates soil movement) and doesn’t corrode from hard water. But PEX isn’t immune — improperly installed fittings or manufacturing defects can still fail.
The Self-Diagnosis Steps
Step 1: Check Your Water Bill
Pull up your last 3-4 months of water bills. Is usage trending up? A slab leak on a supply line can waste 1,000-10,000+ gallons per month depending on severity. At Austin Water’s tiered rates, that’s $10-$100+ in extra charges per billing cycle. A sudden spike with no explanation is the most common first indicator.
Step 2: Do the Meter Test
Turn off every water-using fixture and appliance in the house. Faucets, toilets, dishwasher, washing machine, ice maker, irrigation system, hose bibs — everything. Go to your water meter at the street. Open the meter box and look at the flow indicator (the small triangle or dial on the meter face). If it’s moving, water is flowing somewhere in your system. Since everything in the house is off, that water is going somewhere it shouldn’t.
Step 3: Walk the Floors
Take off your shoes and walk every room of the house slowly on the bare floor. You’re feeling for: warm spots (a hot water line leak heats the slab above it), damp spots (water seeping up through the slab into flooring material), or cool/clammy spots (water evaporation on the surface creates a cooler zone).
Pay special attention to: bathrooms (where supply lines converge), kitchen, laundry room, and the area near the water heater (where supply lines originate).
Step 4: Listen
At night when the house is quiet, walk through and listen near the floor and walls. A slab leak sometimes produces an audible hissing or rushing sound that’s only noticeable when there’s no background noise.
Step 5: Look for Secondary Damage
Walk the perimeter of the house and look at the foundation. New cracks or widening of existing cracks, especially if they’ve appeared or grown recently, can indicate soil movement caused by water saturation under the slab. Inside, check baseboards for warping, walls for new cracks (especially diagonal cracks near door/window frames), and doors/windows for new sticking or alignment issues.
What to Do If You Suspect a Slab Leak
Don’t panic. Don’t start jackhammering. A suspected slab leak needs professional leak detection before any repair decisions are made.
Step 1: Call a plumber for leak detection. At Ironclad, detection runs ~$350. The tech uses electronic listening equipment, pressure testing, and sometimes thermal imaging to pinpoint the leak location without cutting into the slab. This is a diagnostic, not a repair.
Step 2: Once the leak is located, the plumber presents repair options. There are three:
Spot repair (~$2,000): Cut through the slab at the leak location, repair or replace the damaged pipe section, patch the concrete, repair the flooring. Best for: a single isolated leak on an otherwise healthy pipe system.
Reroute (~$3,500): Abandon the damaged under-slab pipe, cap both ends, and run a new line through the attic or walls to bypass it. Best for: a leak in a location that’s difficult to access through the slab, or when the plumber suspects more leaks may follow on the same line.
Full repipe (~$8,500+): Abandon all under-slab supply piping and run new PEX lines through the attic and walls to every fixture. Best for: systemic pipe failure (multiple leaks, widespread corrosion, polybutylene pipe). Most expensive but most permanent.
Step 3: Ask to see the evidence. Camera footage, pressure test results, listening equipment readings. A good plumber shows you why they’re recommending the option they’re recommending. If someone pushes a $10,000 repipe without demonstrating systemic failure, get a second opinion.
The Cost of Waiting
Slab leaks don’t fix themselves and they get worse over time. Here’s what happens if you ignore the signs:
Month 1-2: Water bill increases $30-$80/month. Leak is small. No visible damage yet.
Month 3-6: Water saturates the soil under the slab. Clay soil expands. Foundation begins to shift. Flooring may feel uneven. Hairline cracks appear in walls. Moisture reaches the surface in some areas. Water bill increase is now $50-$150/month.
Month 6-12: Foundation damage becomes significant. Doors stick. Cracks widen. Flooring is visibly damaged. Mold may be growing under flooring or in wall cavities. The $2,000 spot repair is no longer sufficient because the foundation itself may need leveling ($3,000-$10,000+).
Year 1+: Foundation damage, mold remediation, flooring replacement, wall repair. A $2,000 problem became a $20,000-$50,000 problem because it wasn’t caught or was ignored.
The winter average impact: If the slab leak runs through December-February, your Austin Water winter average gets inflated, raising your sewer charges for the entire following year (see our Austin Water Bill Guide).
Ironclad Plumbing: (833) 597-1932. No service visit fees. We’ll find the leak and show you exactly what’s happening before recommending anything.