Water Leak Detection Services: When to Call and What to Expect

A water meter that moves with all fixtures off confirms a leak — but a standard plumbing inspection can’t always find where. Professional leak detection uses acoustic sensors, pressure testing, and thermal imaging to locate leaks inside walls, under slabs, and underground without tearing out materials blindly. Here’s what leak detection services do and when they’re worth calling.

What Is a Water Leak Detection Service?

A leak detection service is a specialized plumbing service — sometimes a separate company, sometimes a division of a plumbing company — that uses diagnostic equipment to find leaks without opening walls or excavating blindly.

Standard plumbing services locate visible leaks: dripping faucets, obvious wet spots, active drips. Leak detection services find hidden leaks: under concrete slabs, inside walls with no visible moisture, in underground service lines, and in irrigation systems.

When the water meter confirms a leak but you can’t find it:
1. Visual inspection finds nothing
2. Basic plumber inspection finds nothing
3. Leak detection service locates it using equipment

What detection services provide:
– Confirmed leak location (usually within 1–2 feet)
– Often: a written report with documentation
– Sometimes: the repair (if they’re also a plumbing service)
– Always: the specific location to open or excavate, minimizing unnecessary damage

How Does Leak Detection Work?

Acoustic leak detection (most common method):
Electronic acoustic equipment amplifies the sound of water escaping under pressure through a pipe crack. The detector identifies the point of maximum sound intensity — which correlates with the leak location. Works best on pressurized lines; less effective on drain lines.

Pressure testing:
The plumber isolates sections of the system and pressurizes them to standard household pressure (or above), then monitors for pressure drop. If pressure drops, that section has a leak. This method confirms which zone has the leak and narrows the search area.

Thermal imaging:
An infrared camera shows temperature differentials. Wet areas register differently than dry areas — cold water leaking behind a wall creates a detectable temperature signature. Most useful for leaks in finished walls or under flooring.

Tracer gas (helium/hydrogen):
A non-toxic tracer gas is introduced to the pipe system. The gas escapes through the leak and rises to the surface. A sensor at the surface detects the gas concentration — pinpointing the leak location even underground. Used for slab leaks and buried service lines.

Endoscope/camera inspection:
A camera is fed through the pipe to visually inspect the interior. More common for drain and sewer lines than pressurized supply lines, but useful for specific situations where visual confirmation is needed.

When to Call a Leak Detection Service

Call leak detection when:
– Water meter confirms a leak (moves with all fixtures off) but visual inspection finds nothing
– Water bill spiked unexpectedly and no obvious cause was found
– You can hear water running inside a wall or floor but can’t locate it
– Wet spots appear on ceilings or floors with no apparent source
– A slab leak is suspected (crack in foundation, warm floor in one area)
– Service line leak is suspected (meter moves with house valve closed)
– After a pipe repair, the meter still shows flow

Don’t need professional detection:
– Active visible drip from a known location
– Running toilet (food coloring test identifies this)
– Leaking faucet (visible source)
– Fresh water damage with obvious cause

The threshold for calling: If you’ve done the basic checks (meter test, toilet dye test, visual inspection of accessible areas) and can’t find the leak, professional detection saves more money than it costs. Opening a wall in the wrong place costs more than the detection fee.

Leak Detection Service Cost in Seattle

Seattle area rates (2026):

What’s included at this price:
– The diagnostic service — location of the leak
– Sometimes a written report with photos
– Usually does NOT include the repair (repair is quoted separately)

Repair cost is separate: Leak detection tells you where the leak is; the repair cost depends entirely on what’s found:
– Wall pipe repair: $400–$1,500
– Slab penetration and repair: $1,500–$5,000
– Service line excavation and repair: $3,000–$12,000

Use the cost estimator for current Seattle rates.

Slab Leak Detection

Slab leaks are the most common reason Seattle homeowners call leak detection services.

What a slab leak is: A leak in a supply or drain pipe embedded in or below the concrete slab foundation. The water escapes into the soil below the slab or up through cracks.

Signs of a slab leak:
– Warm or hot floor in one area (from a hot water line leak)
– Sound of running water under the floor with all fixtures off
– Wet spots or cracks appearing in the slab or flooring
– Sudden water bill increase with no visible source
– Drop in water pressure

Why slab leaks require professional detection: You cannot see the pipe; the leak can travel significant distances from the breach before becoming visible at the surface. Acoustic detection or tracer gas locates the actual pipe breach, not just where the water emerged.

Slab leak repair options:
– Spot repair: Jackhammer through the slab at the leak location, repair the pipe section, re-pour concrete — $1,500–$5,000 depending on depth and access
– Re-route: Run new pipe above the slab through walls or ceiling, bypass the slab section entirely — $2,000–$6,000 and avoids future slab penetrations
– Full repipe: Replace all supply piping with PEX running above the slab — $8,000–$18,000, eliminates future slab leak risk

Underground Service Line Leak Detection

Service line leaks — between the meter and the house — require specialized detection.

Why service line leaks are hard to find:
– The pipe is underground (typically 18–36 inches deep in Seattle)
– Water escapes into the soil and may surface far from the actual leak
– Wet ground can be from multiple sources (rainwater, irrigation, neighbor’s system)

Detection method: Acoustic sensors placed at accessible points (meter, house shutoff, any access points) detect the sound signature of water escaping under pressure. Tracer gas is used for deeper or longer service lines.

Confirmation: Shut the house valve and check whether the meter still moves. If yes, the leak is in the service line. Detection pinpoints where in the line.

Service line repair:
– Spot excavation and repair: $2,000–$5,000
– Full service line replacement: $4,000–$12,000 depending on length and depth
– Trenchless replacement (pipe bursting or slip lining): sometimes available as a less-invasive alternative

How to Prepare for a Leak Detection Appointment

Before the technician arrives:
– Know your meter reading and the results of any meter tests you’ve run
– Know when the problem started (sudden vs. gradual)
– Know which areas of the house you’ve already checked
– Have the main shutoff accessible and operable
– For slab leak suspicion: note which floor areas are warm or wet

During the appointment:
– The technician will typically run through the basic water meter test first
– Acoustic detection may require the house to be quiet (air conditioning, washing machines off)
– The technician may need access to multiple areas — crawl space, basement, under sinks
– Allow 1–3 hours depending on the complexity of the situation

After detection:
– Get the location documented (photos, written description, marked on a floor plan if possible)
– Get a quote for the repair — the detection service may offer it, or you may want competing quotes from plumbers
– Understand what access is needed for the repair (wall opening, excavation, jackhammer)

DIY Leak Detection vs. Professional Services

What you can do yourself:
– Water meter test: confirm an active leak exists (all fixtures off, watch meter for 20 min)
– Toilet dye test: rule out running toilets as the source
– Visual inspection of crawl space, under sinks, around water heater
– Walk the service line path looking for wet ground

What requires professional equipment:
– Acoustic location of a leak inside a wall or under a slab
– Tracer gas for underground lines
– Thermal imaging for hidden wall leaks
– Pressure testing of isolated system sections

The DIY-to-pro handoff point: Once you’ve confirmed a leak with the meter test and ruled out the obvious sources (toilets, visible drips, crawl space), you’re at the limit of what DIY inspection can accomplish. Professional detection equipment costs $5,000–$25,000 — the detection service fee pays for access to that equipment for one job.

Cost comparison: Opening the wrong wall costs $500–$1,500 in drywall work. Professional detection ($300–$600) plus targeted opening at the right location costs less and causes less damage than exploratory opening without detection.

FAQ

Q: When should I call a leak detection service?
A: When your water meter confirms an active leak (moves with all fixtures off) but visual inspection can’t find it. Particularly for leaks under slabs, inside walls, in underground service lines, or after basic DIY inspection finds nothing.

Q: How much does leak detection cost in Seattle?
A: Standard detection: $250–$450. Slab or underground service line detection: $350–$650. Full detection with written report: $400–$800. Detection cost is separate from repair cost — detection tells you where the leak is; the repair is quoted separately.

Q: How does acoustic leak detection work?
A: Electronic sensors amplify the sound of water escaping through a pressurized pipe crack. The technician moves sensors around the floor or wall surface to find the point of maximum sound intensity, which correlates with the leak location. Accurate to within 6–18 inches on a slab.

Q: What’s a slab leak and how is it detected?
A: A slab leak is a leak in a supply pipe embedded in or below the concrete foundation. Signs include warm floor areas, sound of running water under the floor, and sudden bill spikes. Acoustic sensors or tracer gas locate the breach point; repair requires jackhammering to the pipe or re-routing above the slab.

Q: Can I detect a water leak myself without professional equipment?
A: You can confirm a leak exists (meter test) and rule out obvious sources (toilet dye test, visual inspection). Locating hidden leaks inside walls, under slabs, or underground requires acoustic sensors and tracer gas equipment — this is where professional detection services are necessary.