Slab Leak Repair
Updated November 6, 2026
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Safety
If a slab leak is suspected, shut off the main water supply to limit damage and keep everyone away from standing water near outlets, appliances, or the electrical panel. Do not operate electrical devices while standing on wet flooring, and avoid pulling up carpet or tile that may be concealing pooled water. If water is approaching the water heater, furnace, or breaker box, cut power at the panel only if it is dry and safe to reach; otherwise contact the utility. Gas odors, sparking outlets, or a rapidly flooding area call for immediate emergency assistance rather than waiting for a scheduled visit.
Before the visit
Before a technician arrives, close the main water valve and record the meter reading to confirm flow has stopped. Clear access to the water heater, attic hatch, garage, and any rooms where warm spots, dampness, or sounds of running water were noticed. Gather helpful details such as the home's age, pipe material if known, recent water bills, and photos or video of damaged flooring or cracks. Move fragile items out of affected rooms, secure pets, and be ready to discuss whether a spot repair or a reroute fits the situation.
Repair vs replace
Repair is often suitable when the leak is isolated to one accessible point, the remaining under-slab lines pass pressure or isolation testing, and the pipe material is otherwise sound. Common approaches include opening a small section of slab to reach the failure, installing a code-approved fitting or coupling, or rerouting the line through a wall or attic to bypass the slab entirely. Electronic leak detection and pressure testing help a technician confirm that a single-point fix will hold.
When to replace
Repiping or replacement is generally considered when multiple leaks have occurred, pipes show widespread corrosion or repeated pinholing, or the system contains deteriorated galvanized steel or failing polybutylene. Homes with chronic slab leaks, persistent low pressure from mineral buildup, or original plumbing past its service life may be better served by new lines routed above the slab. When the cost of repeated spot repairs approaches the cost of new piping, a full or partial repipe is usually the more durable option.
Common issues
| Symptom | Likely causes | Safe check | Stop when |
|---|---|---|---|
| Warm spots on the floor | A hot water line leaking beneath the slab transfers heat into the concrete and flooring above it. | Walk barefoot across hard flooring and note areas that feel warmer than surrounding surfaces, then compare against where hot water lines are typically routed. | The warm area expands, flooring becomes damp or discolored, or the water heater runs constantly without hot water being drawn. |
| Unexplained spike in the water bill | Continuous water loss through an under-slab leak registers as higher usage even when every fixture is off. | Close all fixtures and the main valve, then watch the meter; movement with the water off points to a leak. Compare recent bills for sudden jumps. | The meter spins quickly with the main valve open, or bills keep climbing after faucet, toilet, and irrigation leaks have been ruled out. |
| Sound of running water with fixtures off | Pressurized water escaping a buried line can create a faint hissing or trickling noise under the floors. | During a quiet period, shut off appliances and fixtures and listen near the floor, especially along walls where supply lines run. | The sound grows louder, water pressure drops noticeably, or dampness appears on flooring or baseboards. |
| Cracked tile, flooring, or baseboards | Escaping water can erode supporting soil, letting the foundation shift and fracture brittle floor materials and trim. | Photograph new cracks and monitor whether gaps widen over several days; also check doors and windows for new sticking. | Cracks spread quickly, floors become uneven or sloped, or doors and windows no longer close properly. |
| Damp carpet or warped flooring | Moisture wicking up through the slab can soak carpet padding and cause hardwood or laminate planks to buckle. | Feel along carpet edges and padding for moisture without tearing up flooring, and check hard floors for cupping or lifting at the seams. | Standing water appears, a musty or moldy odor develops, or flooring separates from the subfloor. |
| Low water pressure or discolored water | A leaking supply line diverts flow and reduces pressure, while corrosion in aging pipes can tint the water rust-colored. | Compare pressure at several fixtures, run cold water to see whether discoloration clears, and note if pressure falls further when a second fixture opens. | Pressure drops sharply, discoloration persists, or multiple fixtures are affected at the same time. |