Home Inspection Plumbing Checklist (2026)

A home inspection plumbing checklist is the difference between buying a house and buying a house plus a $15,000 surprise. Plumbing problems are among the most common — and most expensive — defects inspectors find, yet most buyers have no idea what the inspector is actually looking at. This guide walks you room by room through what a professional inspects, the red flags that should make you pause, and the exact questions to ask before you commit.

What Inspectors Actually Check

First, understand the limits. A general home inspection is visual and non-invasive: the inspector looks at what is accessible, runs fixtures, and reports what they can see. They do not cut into walls, do not pressure-test supply lines, and typically do not run a camera down the sewer line (that is a separate, add-on service worth every penny on older homes).

That said, a thorough inspector evaluates:

• Supply piping — material (copper, PEX, CPVC, galvanized, polybutylene), visible condition, and any active leaks at joints and connections
• Drain, waste and vent (DWV) piping — material (ABS, PVC, cast iron), supports, sagging, and signs of past or active leaks
• Fixtures — every sink, toilet, tub, and shower is run: flow, drainage, leaks at bases and supply connections
• Water heater — age, capacity, venting, TPR valve, drain pan, and signs of corrosion or past leaking
• Functional flow and pressure — running multiple fixtures at once to check for pressure drops and slow drainage
• Sump pumps, shutoff valves, and exterior hose bibs — where present and accessible

The inspector's report flags material defects — things that are unsafe, not working, or near the end of life. Your job as a buyer is to translate those findings into dollars and decisions, which is what the rest of this checklist helps you do.

Kitchen Plumbing Checks

The kitchen concentrates more plumbing connections than any other room, so start here:

• Under-sink cabinet: look for water stains, warped cabinet flooring, and musty smells — the classic signs of a slow supply or drain leak. Feel the P-trap and supply connections for moisture.
• Faucet: run hot and cold at full flow. Check for steady pressure, smooth handle operation, and leaks at the base and sprayer hose.
• Drainage: fill the sink and release — it should drain briskly without gurgling. Gurgling suggests a venting problem (see our guide on drain troubleshooting).
• Dishwasher: check the supply line and drain connection under the sink; look for an air gap or high loop on the drain hose (code requirement in most areas).
• Garbage disposal: run it and listen for excessive vibration or grinding; check for leaks at the sink flange and dishwasher connection.
• Refrigerator water line: if there is an ice maker, trace the small supply line — saddle valves (the clamp-on type) are a red flag; they leak eventually and many plumbers recommend replacing them.

Bathroom Plumbing Checks

Every full and half bath gets the same treatment:

• Toilets: flush each one and watch the base — rocking or water seepage at the floor means a failed wax ring, a cheap fix that causes expensive subfloor rot if ignored. Check the tank fill valve shuts off completely (no running water sounds after the fill).
• Sinks and tubs: run water and check drain speed; look under vanities for stains and active drips; test tub/shower diverters.
• Shower valves: verify hot and cold both work and the temperature is stable — a valve that only delivers scalding or freezing water may need a new cartridge or pressure-balancing valve.
• Caulk and grout: missing or cracked caulk around tubs and shower bases lets water into walls — one of the most common inspection findings and a mold risk.
• Ventilation: confirm exhaust fans vent to the exterior (not into the attic), which matters for moisture control around plumbing.

Basement, Crawlspace and Attic

This is where the inspector earns their fee. Exposed piping tells the story of the whole system:

• Pipe material identification: black plastic is ABS, white plastic is PVC, flexible red/blue is PEX, dull gray metal is galvanized steel, greenish metal is copper. Mixed materials with proper transition fittings are fine; mystery patches and rubber "band-aid" couplings are not.
• Active leaks and old stains: any green/white crust on copper (corrosion), rust on galvanized, or water staining on wood near pipes.
• Supports and slope: drain lines need proper hangers and a consistent downward slope — sagging "bellies" in drain lines collect waste and cause chronic clogs.
• Sewer cleanouts: note whether accessible cleanouts exist; their absence makes future drain work far more expensive.
• Attic: check vent pipes penetrating the roof (cracked rubber boots are a top leak source) and look for water stains on the underside of the roof deck near plumbing vents.

If the home was built between the mid-1980s and 1990 and you see black ABS drain pipe, read our ABS pipe lawsuit explainer — pipe from that era has a documented history worth knowing before you buy.

Water Heater and Main Shutoff

• Age: find the manufacturer date on the rating plate. Tank water heaters last 8–12 years; a 14-year-old unit is living on borrowed time and should be budgeted for replacement ($1,200–$3,500 installed, depending on type).
• TPR valve: the temperature-pressure relief valve must have a discharge pipe running down to within 6 inches of the floor — a missing or capped TPR discharge is a safety defect.
• Corrosion and leaks: rust streaks from fittings or the tank base, and any moisture in the drain pan, signal a unit near failure.
• Venting (gas units): the flue must slope upward to the chimney or vent, with no gaps or corrosion — backdrafting carbon monoxide is a life-safety issue.
• Main water shutoff: locate it and confirm the valve actually turns. A seized main shutoff is a small fix with outsized importance in an emergency.

Pipe Red Flags by Material

Certain pipe materials deserve extra scrutiny because of known failure modes:

• Galvanized steel supply pipe (common pre-1970): corrodes from the inside, strangling water flow and eventually leaking. Full replacement is usually the only fix — budget $4,000–$15,000 for a repipe.
• Polybutylene supply pipe (1978–1995, usually gray or blue plastic): notorious for sudden, catastrophic failure. Many insurers surcharge or decline homes with it. See our polybutylene guide for identification and replacement costs.
• Cast iron drain pipe (pre-1980): lasts 50–80 years but eventually scales, cracks, and collapses. Camera inspection of the main drain is strongly recommended.
• 1984–1990 ABS drain pipe: a documented defective batch prompted a $73.6M class-action settlement; details in our lawsuit explainer.

For a deeper dive on any material, browse our pipe guides library and learn to identify pipe materials yourself.

Questions to Ask Your Inspector

1. "What is the supply and drain pipe material?" — Get it in writing, room by room if mixed.
2. "How old is the water heater, and what is its condition?" — Age plus visible condition tells you whether to budget for replacement now.
3. "Did you see any active leaks or signs of past leaks?" — Past leaks suggest recurring issues worth investigating.
4. "Is there anything here that would make a plumber's follow-up worthwhile?" — Good inspectors will tell you when a $150–$300 plumber visit or sewer camera scope ($100–$300) is justified.
5. "Are the shutoff valves functional?" — Especially the main shutoff.
6. "Do you recommend a sewer line camera inspection?" — On any home older than 25–30 years, the answer should almost always be yes. A collapsed sewer line costs $3,000–$12,000+ to replace; a $200 scope is cheap insurance.

Finally, price what you find. Our plumbing cost guides give verified 2026 ranges for repipes, sewer replacements, water heaters, and common repairs — bring those numbers to your negotiation, not just the inspection report. Plumbing defects are among the most negotiable items in a home purchase because the costs are concrete and quotable.