Plumbing Inspection Checklist: Supply, Drainage, Water Heating, and Fixtures
Plumbing failures cause more insurance claims than any other residential system, and almost all of them trace back to three things: pipe material, water heater age, and a fitting nobody could see. This checklist covers what is observable at a standard inspection, what belongs to a plumber, and the material identifications that change a home's insurability.
Who orders this
Every home inspection and every 4-point. Particularly important on homes built 1978–1995 (polybutylene era), pre-1960 homes (galvanized steel), and any home with a water heater past 10 years.
Water Supply
Identify the material, measure the pressure, and check the flow under simultaneous demand.
- Supply source — municipal or private well
- Main shutoff located, accessible, and operable
- Supply line material at the meter and at fixtures
- Polybutylene (gray or blue flexible pipe, 1978–1995) present
- Galvanized steel and evidence of internal corrosion or restricted flow
- Copper condition, including green corrosion at joints and pinhole evidence
- PEX and CPVC condition and support
- Static water pressure measured at a hose bib (typically 40–80 psi)
- Pressure reducing valve present where supply exceeds 80 psi
- Functional flow with two or more fixtures running simultaneously
- Water hammer on quick valve closure
- Exterior hose bibs — operation, backflow prevention, frost protection
- Visible supply piping in unconditioned space and its insulation
Drain, Waste, and Vent
Run water and watch. Most DWV defects reveal themselves in thirty seconds of observation at the fixture.
- Drain material — cast iron, galvanized, ABS, PVC, or Orangeburg at the lateral
- Cast iron scaling, rust-through, or bellying where visible
- Drainage speed at each fixture and any gurgling
- P-trap present at every fixture
- S-traps, which siphon dry and admit sewer gas
- Trap arm length and slope where visible
- Improper materials or flexible corrugated traps under sinks
- Visible leaks at trap joints, cleanouts, and connections
- Prior repair clamps or tape
- Vent piping visible in attic and its termination through the roof
- Air admittance valves used and whether they are accessible
- Cleanout locations identified
- Sump pump operation, discharge point, and check valve
- Ejector pump for below-grade fixtures
Water Heater
Age from the serial number, then confirm the four safety items. This section produces findings on a large share of inspections.
- Type — tank, tankless, heat pump, or indirect
- Manufacture date decoded from the serial number
- Capacity and energy source
- TPR valve present and rated to the tank
- TPR discharge pipe — full size, downward, rigid material, terminating 6 inches above the floor, not threaded at the end
- Drip pan and pan drain where installed over finished space
- Seismic strapping where required by jurisdiction
- Combustion air provision for gas units in confined spaces
- Flue condition, slope, and connection — no backdrafting evidence
- Corrosion at the tank base, fittings, and connections
- Dielectric unions where dissimilar metals meet
- Expansion tank present on a closed system
- Temperature setting (approximately 120°F to limit scald risk)
- Gas unit located in a garage — ignition source elevation where required
Fixtures and Appliances
Operate everything. Fixture findings are small individually and add up to a meaningful list.
- Every sink, tub, shower, and toilet operated
- Toilets secure to the floor with no rocking
- Toilet flush performance and fill valve shutoff
- Faucet operation, aerator flow, and diverter function
- Shower pan and surround condition, grout and caulk integrity
- Tub overflow gasket leakage evidence at the ceiling below
- Supply stops present at each fixture and not seized
- Under-sink leak evidence and cabinet base staining
- Dishwasher drain high loop or air gap
- Washing machine supply hoses — braided vs. rubber, and their age
- Laundry standpipe height and trap
- Water softener or filtration bypass and condition
Most common findings — and why they matter
These come up often enough that it is worth knowing the consequence, not just the observation.
Polybutylene supply lines
Degrades internally from chlorine exposure and fails without warning. Most carriers decline coverage until the home is repiped.
TPR discharge terminated incorrectly
The most frequent water heater finding. A discharge that is threaded, undersized, upward-sloped, or ending too high converts a pressure relief into a scald hazard.
S-traps under sinks
Self-siphon and let sewer gas into the room. Common in older homes and in DIY vanity replacements.
Missing dishwasher high loop or air gap
Allows drain water to backflow into the dishwasher. Two-minute fix, and it appears in a large share of reports.
Water pressure above 80 psi with no PRV
Accelerates failure of every fitting, valve, and appliance hose in the house. Rarely checked, easily measured.
Frequently asked questions
How do I tell polybutylene from PEX?
Polybutylene is usually dull gray (sometimes blue or black) with a matte finish and stamped 'PB2110'. PEX is glossier, comes in red, blue, or white, and is stamped with a PEX designation and an ASTM F876/F877 reference. When in doubt, photograph the stamp rather than judging by color.
How long does a water heater last?
Tank units typically 8–12 years, tankless 15–20 with maintenance. Water chemistry and whether the anode rod was ever replaced move these considerably. Report the manufacture date and let the reader draw the conclusion.
Do inspectors test for leaks inside walls?
No. Concealed piping is outside every standard of practice. Inspectors report visible evidence — staining, elevated moisture readings, or damage — and recommend further evaluation.
Is galvanized supply piping a required replacement?
Not automatically, but it corrodes internally and progressively restricts flow. Report the material, the observed flow, and any visible corrosion, then let the buyer weigh remaining life against replacement cost.
Turn this checklist into a finished report
Walk the property, photograph what you find, and narrate your observations. FieldScribe analyzes the photos, transcribes the voice notes, and drafts the report in professional language — you review, edit, and export the PDF. First report is $9.99 with no subscription.
Related checklists
This checklist is provided free for professional and personal use. It is a general reference, not a standard of practice — inspection requirements vary by state, jurisdiction, and client agreement, and licensing rules for specialty inspections differ. Verify current requirements with your state board and the relevant standard of practice before relying on it in the field.