A slab leak is a water line failure underneath the concrete foundation. Because you can't see it, homeowners usually notice the side effects for weeks before they work out what's causing them.
This is the most common first clue. Nothing about the household changed, no fixtures are obviously running, and the bill still climbs. A leak under the slab runs continuously, so it shows up as a steady increase rather than a one-off spike.
Turn off every fixture and water-using appliance in the house, then look at the water meter. If the low-flow indicator is still turning, water is moving somewhere it shouldn't be. Note the reading, wait an hour without using any water, and check again — movement with everything off means an active leak, though it doesn't by itself tell you the leak is under the slab.
If the failure is on the hot water side, heat transfers up through the concrete. A patch of floor that's noticeably warmer than the area around it — especially one that stays warm — is one of the more specific slab leak signs there is.
A faint rushing or hissing you can hear in a quiet house, particularly near floor level, is worth taking seriously. It's easiest to notice late at night when the rest of the house is silent.
Water working its way up through the slab shows up as unexplained damp spots at floor level, flooring that lifts or cups, or a persistent musty smell in one area of the house. In Portland's damp months these are easy to blame on the weather, which is part of why slab leaks go unaddressed for so long.
Water moving through the soil under a foundation can shift it. Fresh cracks in walls or flooring, or doors and windows that suddenly bind, can point that direction — though these have plenty of other causes too, so they're supporting evidence rather than proof.
Slab leaks don't resolve on their own, and the damage compounds: wasted water on every bill, moisture in the flooring and subfloor, and eventually movement in the foundation itself. The repair scope also grows the longer the water runs.
Locating the leak comes before any concrete gets opened. Once the line and position are pinpointed, the options are typically a spot repair at that point or rerouting the affected section — which one makes sense depends on the pipe's condition, its location, and how the plumbing is laid out.
Seeing any of these signs? Call us at (971) 386-1515 — we're available 24/7.