Signs of a Slab Leak in Woburn, MA

What are the warning signs of a slab leak?

The most common signs of a slab leak are a higher water bill, the sound of running water when everything is off, warm spots on the floor, damp or buckling flooring, musty smells, low water pressure, and new cracks in floors or walls. One or two of these together is a strong reason to have your home checked.

A slab leak is a leak in a water or drain pipe under your concrete floor. In Woburn, that includes basement floor slabs, plus ranch homes, additions, garages and condos built on a slab. Because the pipe is hidden, the leak often runs for weeks before anyone notices. Catching it early keeps the repair small and cheaper.

The 7 most common slab leak signs

1. Your water bill jumps for no reason. A leak runs 24 hours a day. If your bill climbs but your water use hasn't changed, water is escaping somewhere.
2. You hear running water with everything off. Turn off all taps and appliances and listen near the floor. A faint hiss or trickle can be water escaping under the slab.
3. There's a warm spot on the floor. A warm or hot patch on tile, wood or carpet often means a hot water line is leaking below. This is one of the clearest signs.
4. Flooring is damp, cupped or loose. Water wicks up into carpet, lifts hardwood, and loosens tile grout and mortar.
5. You smell musty or mildew odors. Trapped moisture under the floor feeds mold and mildew, which you smell before you see.
6. Water pressure drops. A leak bleeds off pressure, so several fixtures feel weak at once.
7. New cracks appear. Water can move the soil under a slab, leading to fresh cracks in the floor, walls or foundation.

Other clues include a water heater that runs constantly (a sign of a hot line leak), pets that keep lying on one warm spot, and mold along baseboards. Learn how the leak is pinpointed on our slab leak detection page.

How can I check for a slab leak myself?

Use the water meter test. Turn off every faucet, appliance and outside hose. Write down your water meter reading or take a photo. Wait 1 to 2 hours without using any water, then read the meter again. If the numbers moved, water is leaking somewhere in your home.

1. Shut off all water. Inside and outside, including the ice maker and any humidifier.
2. Read the meter. Note the numbers or the position of the small leak-indicator dial.
3. Wait and re-check. Come back in 1 to 2 hours. Movement means a leak.
4. Test hot vs. cold. Close the cold-water valve on top of your water heater and repeat. If the meter stops, the leak is likely on the hot side.

The meter test tells you that you have a leak. It can't tell you exactly where. That's what a plumber's detection tools are for.

Warm floor or hot water sign? Act quickly

A warm spot usually points to a hot water slab leak. These waste both water and the energy used to heat it, and they can wear out your water heater. If a spot on your floor stays warm and you don't have in-floor radiant heat, treat it as urgent.

How long can a slab leak go undetected?

A slab leak can go undetected for weeks or months, and sometimes longer if it's a slow drip. Slow leaks may only show up as a gradually rising water bill. The longer a leak runs, the more it damages flooring, walls and the soil under your foundation, and the more the repair costs.

What to do if you see the signs

1. If water is visible, shut off your main water valve, usually in the basement near the meter.
2. If the floor is warm, switch your water heater to "pilot" or "vacation," or turn off its breaker.
3. Book detection. A plumber confirms and pinpoints the leak. See slab leak detection.
4. For water on the floor now, see emergency slab leak repair and call (781) 483-8802.

Wondering who pays? Read our guide on whether a slab leak is covered by insurance.