Leak Detection
Updated November 6, 2026
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Safety
If water is actively pooling or a pipe has burst, close the main water shutoff valve first. Keep lamps, cords, and appliances away from standing water, and cut power at the breaker to any room where outlets or fixtures are wet. Stay out from under ceilings that sag, bulge, or drip, since trapped water can bring drywall down. Never dig near buried lines or open walls to chase a leak; pressurized plumbing and any gas-adjacent work belong to trained professionals.
Before the visit
Write down where and when moisture appears, and photograph stains, damp spots, and the water meter. Locate the main shutoff and confirm it turns freely. Clear access to under-sink cabinets, the water heater, appliances, and any crawl or attic hatches near the suspected leak. Keep recent water bills on hand if usage has climbed, and note any prior repairs on the affected lines.
Repair vs replace
Repair is typically the right call when a leak is isolated to one fitting, valve, fixture seal, toilet flapper, or an accessible stretch of pipe, and the surrounding materials remain sound. Pinhole leaks, dripping supply lines, and worn shutoff valves usually respond well to targeted fixes rather than replacing whole systems.
When to replace
Replacement tends to make more sense when pipes show widespread corrosion, new leaks keep appearing along the same run, a water heater tank is rusted or past its expected lifespan, or slab leaks return after earlier repairs. Saturated drywall, insulation, or subflooring may also justify replacing entire sections instead of patching repeatedly.
Common issues
| Symptom | Likely causes | Safe check | Stop when |
|---|---|---|---|
| Water meter moves while every fixture is off | Hidden supply-line leak, running toilet, slab leak, or a break in an irrigation or service line | Shut off all faucets and appliances, write down the meter reading, avoid water for 30 to 60 minutes, then compare readings | Water is surfacing indoors or the dial spins fast, which suggests an active break |
| Warm or damp spots on floors | Hot water slab leak under flooring or a failing hot water line in or beneath the slab | Compare floor temperatures by hand and watch whether the water heater runs constantly with no hot water drawn | Flooring buckles, tiles loosen, or warm areas spread from day to day |
| Running or dripping sounds inside walls | Pinhole leak in a supply pipe, failed joint, or a toilet fill valve that never fully seals | Listen near fixtures with all water off; a hiss or trickle at the wall points to a pressurized leak | Drywall feels soft, stains spread, or the sound becomes a steady rush |
| Musty odors or recurring mold | Slow drip behind walls, under sinks, or beneath cabinets keeping materials damp | Shine a flashlight under sinks, around appliance hoses, and along baseboards for discoloration or dampness | Mold spreads across a large area or household members develop breathing irritation |
| Sudden jump in the water bill | Underground service line leak, running toilet, irrigation leak, or a water softener stuck in a cycle | Compare several months of bills and run the meter test with all fixtures off | Usage stays high with no visible leak, which often means a buried line is involved |
| Stains, bubbling paint, or warped drywall on walls and ceilings | Leaking pipe joint, roof or upstairs plumbing leak, or condensation from a sweating line | Mark the stain's edge, check the room above, and watch for 24 to 48 hours to see whether it grows | The ceiling sags, drips steadily, or gives when pressed |
| Soggy yard patches or unusually lush grass | Buried water service line leak or a cracked irrigation line | Note whether the wet area persists through dry weather and whether it follows the path of the main line | Water pools quickly, the ground sinks, or the area sits near the foundation |