Plumbing Inspection Checklist: What to Check Before You Buy

Plumbing problems are particularly cruel to first-time buyers because they are often invisible until they fail catastrophically. A sewer line collapse happens underground. Polybutylene pipes degrade from the inside out. A corroded galvanised supply line looks fine from the outside while delivering rust-brown water to the tap. A thorough plumbing inspection before you buy is one of the highest-value forms of due diligence you can perform — and much of it you can do yourself during a showing, before you've spent anything on professional reports.

Part 1: Pipe Material Identification

The single most important question in a plumbing inspection is: what are the pipes made of? Different materials carry different risk profiles, insurance implications, and estimated remaining service lives.

Supply Lines (What Brings Water In)

Copper — The gold standard. Copper supply piping installed after the 1960s in good condition has a service life of 50–70 years. Look for blue-green staining at joints, which indicates pinhole leaks developing from internal corrosion. Copper in acidic water environments (common in some parts of the Pacific Northwest) can fail faster.

CPVC (Cream or beige plastic) — A modern, code-compliant material. Generally reliable but becomes brittle with age and in cold climates. Check for cracks at fittings and at any locations where the pipe has been exposed to freezing.

Galvanised steel (silver-grey metal) — Common in homes built before 1960. Galvanised pipes rust internally, gradually reducing water pressure and eventually failing. The diagnostic test: run the hot water at the bathtub full flow for 30 seconds, then observe. If the flow starts strong and drops to a trickle, the interior of the pipe is heavily corroded. Replacement of galvanised supply lines in a typical house costs $4,000–$10,000 depending on the extent.

Polybutylene (grey flexible plastic, sometimes with grey fittings) — Used extensively from 1978 to 1995. This is the most significant red flag in supply plumbing. Polybutylene reacts with chlorine in municipal water supplies, degrading from the inside until the pipe splits — typically at fittings and elbows, inside walls and ceilings. It is now uninsurable in many markets. Full repiping costs $6,000–$15,000. Some insurers will decline coverage entirely. If you identify grey plastic supply pipes, confirm the material before proceeding.

PEX (flexible coloured tubing — red for hot, blue for cold, or white) — The modern standard for residential plumbing. Flexible, freeze-resistant, and long-lived. Generally positive if present.

Drain, Waste, and Vent Lines

PVC (white plastic) — Modern standard. No concerns.

ABS (black plastic) — Standard in Canada and common in the western US. No concerns if installed correctly. Check for "spider cracking" — a fine web of surface cracks indicating the material has become brittle.

Cast iron — Common in pre-1980 homes. Cast iron drain lines rust from the inside, a process called "channelling" where the bottom of the pipe corrodes away. This is not visible without a camera. Any home built before 1980 with cast iron waste lines should have a sewer scope as an inspection add-on.

Orangeburg (black, fibrous, paper-like) — Used from the 1940s through the 1970s as a cheap wartime alternative to cast iron. It absorbs moisture and collapses inward over time. If you see black pipe material that looks fibrous or cardboard-like in the basement or crawlspace, this is a significant problem requiring immediate replacement.

Part 2: The Pressure and Flow Tests

During your showing — or as part of a formal inspection — run these tests:

Kitchen faucet: Turn on cold full blast, then hot full blast. Check pressure, and check for rust colour in the first several seconds of hot water flow (indicates galvanised pipes).

Shower and tub: Run both simultaneously with the kitchen faucet. If pressure drops significantly, the supply lines or the main pressure-reducing valve may be failing.

Toilet flush: Flush each toilet and observe that the tank fills within 60 seconds and the bowl seals completely. A "running" toilet isn't a major expense, but multiple running toilets indicate deferred maintenance.

Drain speed: Fill each sink and tub to a few inches and drain. A slow drain is not always a major plumbing issue — it could be a simple hair clog — but systematically slow drains throughout the house suggest a drain line slope problem or partial blockage deeper in the system.

Check under every sink cabinet: Look for water stains, swollen particleboard, rusted drain rings, or a bucket that has "mysteriously" appeared under the pipe. These are universal signs of a known, recurring leak.

Part 3: Water Heater Assessment

The water heater is one of the most reliably age-able components in the home. Find the data plate on the unit and note the serial number. Most manufacturers encode the manufacture date in the first characters — a quick web search for the brand name and "serial number date code" will give you the decoding key.

Standard tank water heaters have an average service life of 10–15 years. If the unit is over 15 years old, budget for replacement regardless of its current condition — it is operating on borrowed time.

Signs of imminent failure:

• Rust-coloured water from hot taps (internal tank corrosion)
• Rust streaks down the outside of the tank at the bottom (bottom corrosion through the tank wall)
• Rust or mineral buildup around the top connections
• A popping or rumbling sound during heating (sediment buildup on the heating element)
• A missing or incorrectly installed Temperature Pressure Relief (TPR) valve discharge tube — this is a safety issue. The tube must extend to within six inches of the floor and discharge downward.

In Canada and the northern US, also check whether the water heater is in a heated space or an uninsulated location where freeze damage could occur.

Part 4: Septic System Inspection Checklist

If the property is on a septic system rather than municipal sewer, the inspection scope expands significantly. Septic failure is expensive — a full replacement runs $10,000–$30,000 depending on the system type and soil conditions — and in many markets the seller is required to disclose the system's age and last service date, but not necessarily its condition.

A basic septic system inspection checklist covers:

Above-ground indicators:

• Is the area over the drain field noticeably greener or wetter than surrounding ground? This indicates the system is overwhelmed and surfacing effluent.
• Are there odours near the drain field or around the tank lids?
• Are the tank lids present, intact, and accessible?

Tank inspection (requires pumping or inspection access):

• When was the tank last pumped? Recommended interval is every 3–5 years for a family-sized home.
• What is the scum and sludge depth? If the combined depth exceeds one-third of the tank capacity, the tank needs immediate pumping.
• Are the inlet and outlet baffles intact? Broken baffles allow solids to exit into the drain field, which clogs it.
• What is the tank material? Concrete (durable), fibreglass (durable), or steel (corrodes — check for holes and rust)? A steel tank past 25 years is likely failing.

Drain field:

• Request documentation of the drain field location — many homeowners don't know where it is.
• Is the drain field area compacted by vehicle traffic, which crushes the distribution lines?
• Has any construction, landscaping, or planting occurred over the drain field in recent years?

In the UK, septic tanks discharging to surface water rather than soakaway were required to be upgraded by 2020 under Environmental Agency regulations. Verify compliance before purchase.

In rural Canada and Australia, also check the system capacity relative to the bedroom count — many older systems are undersized for modern household water usage.

Part 5: Indicators That Warrant a Sewer Scope

Even on municipal sewer, the underground line from the house to the street is the homeowner's responsibility — typically for the full length of the lateral to the city main. Sewer line failures are the single most common "expensive hidden repair" cited by homeowners in the first year of ownership.

Order a sewer scope camera inspection (typically $150–$250 as an add-on) if the home meets any of these criteria:

• Built before 1980 (cast iron or Orangeburg drain lines)
• Large trees — particularly willows, poplars, or oaks — near the drain path to the street
• Any evidence of basement sewage backups (staining near floor drains, damaged floor tiles near the drain)
• The seller is unable to provide a recent clean inspection or pump-out record for the main line

The Home Inspection Checklist includes a complete plumbing section covering pipe material identification with photographs, a water heater age and condition assessment, the septic system checklist above, and a repair cost matrix for each finding — so you can translate defects into negotiation credits on the spot.