Supply Line vs Irrigation vs Condensate Source Isolation Decision Tree

Why this matters

When the homeowner walks you into a wet baseboard or a soaked carpet pad and says "I have no idea where this came from," the cause analysis decides the category, the insurance coverage path, and whether you start drying or start ripping. A pinhole copper supply leak is Cat 1 and a plumber's repair. An irrigation backfeed through a wall penetration is Cat 1 from a clean source but moves to Cat 2 fast as it traverses lawn soil. A condensate overflow is Cat 1 on the first day, Cat 2 in 48 hours. Calling source wrong on the first visit is the single biggest reason restoration jobs blow scope by Day 3.

Symptom presentation

Three patterns dominate the cause-unknown intake. Pattern one is interior wet drywall along an interior wall with no fixture nearby, dry exterior side, no recent storm. Pattern two is wet exterior wall at grade with irrigation zones running every other day, no visible plumbing. Pattern three is a wet ceiling under a second-floor HVAC closet or a wet ceiling under a slab-mounted air handler with no obvious leak above.

Pattern one usually traces to a hot or cold supply line in the wall cavity, slab leak under a kitchen or bath, or rare pinhole at a recessed valve. Pattern two usually traces to irrigation lateral leak, broken sprinkler riser inside a planter against the house, or a clogged downspout backflowing. Pattern three usually traces to a condensate drain line, primary or secondary pan overflow, evaporator coil sweat with a missing or stripped insulation jacket.

Quick checks

Test water chemistry at the source. Strip-test pH, chlorine, and TDS. A supply leak reads pH 7.0 to 8.5, TDS 100 to 600 depending on municipal source, chlorine detectable. Irrigation reads same as supply if on potable feed; reads much lower chlorine and higher TDS if on well or reclaimed. Condensate from an evaporator coil reads pH 6.5 to 7.5 with near-zero TDS and zero chlorine because it is distilled water from condensation.

Read the meter test on the supply. With every fixture off, watch the leak indicator on the water meter for 15 minutes. Any spin confirms a supply-side leak somewhere in the house service. No spin pushes the source toward irrigation, condensate, or other non-pressurized origins.

Pull a small inspection hole in the wettest wall cavity. The leak source pattern is usually visible inside 60 seconds. Drip from above is a supply line above the cut. Wick from below is slab or grade. Drip from a horizontal nail-plate area is supply at a stud bay.

Isolation tree

Branch A: meter spins with every fixture off. Supply leak. Isolate by closing the home shutoff and checking whether the meter stops. Stop means leak is house-side. No stop means leak is between meter and shutoff (city responsibility). Drop the loss to a plumber for source repair; restoration proceeds in parallel.

Branch B: meter does not spin, leak only when irrigation cycles. Irrigation source. Walk the zone schedule with the controller. Run each zone manually for 5 minutes while watching the wet area. Confirm the offending zone and have irrigation tech repair before drying. Note category: clean irrigation supply is Cat 1, but transit through soil or onto a contaminated patio elevates it to Cat 2 within hours.

Branch C: meter does not spin, leak only when HVAC runs in cooling mode. Condensate source. Check primary drain pan for standing water with the unit cooling. Check secondary safety pan for any accumulation. Look at the line termination outside the house; a free-flowing termination on a cool day rules in condensate. Pour a measured cup of water into the primary pan and watch transit time to the termination; slow or blocked transit confirms a clog.

Branch D: meter does not spin, no irrigation, leak occurs randomly. Look for a sweating cold pipe in the wall cavity, a missing pipe insulation jacket on a chilled-water line, a refrigerant suction line dripping condensate onto a wall sheathing, or a leaking dishwasher or refrigerator supply behind a kitchen cabinet that only drips when the appliance demands water.

Branch E: meter does not spin, water present only after rain. Roof, flashing, or grade leak. This is not a plumbing source at all; investigate roof penetrations, window flashing, and surface drainage.

Confirming diagnosis

Document the chemistry test with a photograph of the strip alongside a label of where the sample came from. Adjusters challenge source determination more than any other line item; the strip photo is your defense.

Re-test after 48 hours. A supply leak under pressure does not stop until the plumber stops it. A condensate or irrigation source stops when the contributing system is paused. Re-test confirms the cause and prevents the embarrassing day-3 finding that the carpet pad is still wetting.

Map the wet pattern with thermal imaging plus pin meter. Thermal shows the active wet path; pin meter quantifies the wetness. The two together build the cause map in court-quality form.

Remediation

Stop the source before drying. This is non-negotiable. Air movers on a continuing leak just spread the loss; you will be back on Day 2 with a larger affected area and the homeowner will not be happy.

Treat irrigation-sourced water as Cat 2 from the moment it transited soil. PPE accordingly. Apply an EPA-registered antimicrobial to all affected surfaces per S500 protocols for elevated categories.

For condensate sources, also evaluate the HVAC system itself. A clogged drain that overflowed has likely also wetted the cabinet of the air handler and possibly grown microbial film on the coil. Confirm with a borescope check before signing off the cause.

References

1. ANSI/IICRC S500-2021 Standard for Professional Water Damage Restoration, Sections 10.5 (Initial Inspection) and 12.2.3 (Source and Category Determination).
2. ASTM D5851-95 Standard Guide for Planning and Implementing a Water Monitoring Program, source-attribution sampling.
3. EPA Method 9023 Strip Testing, residential potable water characterization references.
4. ASHRAE 62.2 Ventilation and Acceptable Indoor Air Quality in Residential Buildings, condensate drainage requirements.
5. International Plumbing Code Section 314, Condensate Disposal requirements (2024 edition).