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Plumbing Inspection Checklist: What Inspectors Look For (And What Homeowners Miss)

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Plumbing fails quietly. A slow leak behind a wall, a corroded shutoff valve that hasn't been tested in a decade, a drain line with a belly that holds standing water — none of these announce themselves. They show up at home inspection, or worse, after closing.

This checklist covers what a thorough plumbing inspection includes: what the inspector is looking at, what they're testing, and what the findings actually mean. Whether you're buying a home, selling one, or doing a maintenance pass on a house you've owned for years, this is the framework.

How Plumbing Inspections Work

A standard home inspector covers plumbing as part of a general inspection. They're looking at accessible systems — what they can see, reach, and test. They're not pulling permits, snaking drains, or running a camera through your sewer line (that's a separate specialist inspection). They're doing a visual and functional assessment.

A plumbing-specialist inspection goes deeper: sewer scope, pressure testing, detailed assessment of fixtures and supply lines. If a general inspection flags something, this is usually the next step.

What inspectors test:

  • Water pressure at fixtures
  • Hot water function and temperature
  • Drain flow rates (fill and drain at sinks, tubs, showers)
  • Toilet flush and fill function
  • Visible supply line condition
  • Visible drain line condition
  • Water heater operation and safety devices
  • Sump pump function
  • Exterior hose bibs

What inspectors don't do:

  • Open walls
  • Scope sewer lines (unless hired specifically for that)
  • Test shutoff valves under pressure (though they note if they appear seized)
  • Assess underground supply or drain lines

Section 1: Water Supply System

Main Shutoff Valve

The main shutoff valve is the single most important valve in the house. If a supply line bursts at 2am, you need this valve to work immediately and completely.

What to check:

  • Location — Know where it is before you need it. Common locations: basement near the foundation wall where the supply enters, utility room, crawl space, exterior meter box.
  • Operability — Can it be turned? Gate valves (older, multi-turn) sometimes seize from disuse. Ball valves (modern, quarter-turn) are more reliable. If a gate valve is corroded or seized, budget for replacement.
  • Full shutoff — When closed, does flow stop completely at fixtures? A valve that only partially closes is functionally useless in an emergency.
  • Condition — Any signs of active leaking or past drips at the valve body or connections?

Red flag: A main shutoff valve that can't be operated or doesn't fully close. This is a safety issue, not a cosmetic one.

Water Pressure

Residential water pressure should run between 40 and 80 PSI. Below 40 PSI and you'll notice weak flow at showers and hose bibs. Above 80 PSI and you're shortening the life of every appliance and fixture in the house — dishwashers, washing machines, water heaters, and supply lines all have pressure ratings.

What to check:

  • Gauge reading — Use a pressure gauge on a hose bib. This is a $10 tool worth owning.
  • Pressure reducing valve (PRV) — Most homes on municipal supply have one, typically near the main shutoff. PRVs fail over time. If pressure is outside range and there's a PRV, it may need adjustment or replacement. PRV replacement runs $200–$500 installed.
  • Pressure consistency — Does pressure drop significantly when multiple fixtures run simultaneously? Normal to drop slightly; a dramatic drop indicates a supply line sizing or PRV issue.

Red flag: Pressure consistently above 80 PSI without a functioning PRV. Over time this causes pinhole leaks in copper, supply line failures, and shortened appliance life.

Supply Line Material

The material your supply lines are made of tells you a lot about the maintenance history ahead of you.

Copper — The gold standard. Durable, long-lived (50+ years in most conditions), resistant to corrosion. Can develop pinhole leaks in areas with aggressive water chemistry (low pH, high chloramines). Green oxidation (patina) on the outside is normal and protective. White mineral buildup at joints indicates a slow leak.

CPVC — Chlorinated PVC, common in homes built from the 1970s–2000s. Good pressure resistance, but becomes brittle with age and can crack from physical stress or incompatible chemicals (some cleaning products, certain pipe dopes). Inspect for cracks at fittings and joints, especially in older installations.

PEX — The modern standard for new construction and remodels. Flexible, freeze-resistant, easy to install. No known lifespan issues in normal residential use. Different connection types (crimp, clamp, expansion) — all are fine if installed correctly.

Galvanized steel — Found in homes built before 1960. Corrodes from the inside out. The interior oxidation restricts flow (you'll notice low pressure even if municipal supply is fine), and eventually the pipe rusts through. If you have galvanized supply lines, budget for replacement. This isn't a question of if, it's when.

Polybutylene (PB) — Gray plastic pipe common in homes built 1978–1995. PB has a well-documented failure history: the material degrades from chlorine in municipal water, leading to micro-fractures and eventual failure at fittings. It's been the subject of major class action settlements. If you have PB pipe, replacement is strongly recommended. Look for gray plastic pipe with gray, white, or blue plastic fittings (or copper crimp fittings at connections).

What to check:

  • What material is present in visible areas (basement, crawl space, utility areas)?
  • Any signs of repair patches, which indicate a prior leak?
  • Any active drips or staining at joints?
  • For galvanized: is water pressure adequate at fixtures despite good municipal pressure?

Individual Fixture Shutoffs

Every fixture — toilet, sink, dishwasher, washing machine, refrigerator ice maker — should have its own shutoff valve. These allow you to isolate a fixture without shutting off the whole house.

What to check:

  • Are shutoffs present at every fixture?
  • Do they operate? Angle stop valves (the common oval-handle valves under sinks and behind toilets) seize from disuse. If they can't be turned, they'll fail when you need them.
  • Any drips or mineral deposits at the valve body?

Note: Exercising shutoff valves annually (turning off and on) keeps them operable. Many homeowners discover a seized shutoff only when they're trying to replace a toilet at 8pm on a Sunday.

Section 2: Drain, Waste, and Vent System

Drain Flow Rate

Every drain should flow freely with no gurgling, no slow drain, no standing water.

What to check:

  • Fill each sink to the rim, release the stopper, and watch the drain rate. A healthy drain empties a full sink in under 30 seconds.
  • Showers and tub drains: run water for 2 minutes and watch for backup or slow clearing.
  • Toilet: flush and confirm complete clearing on a single flush.

Slow drain causes:

  • Localized clog — hair, soap buildup, grease in a trap or branch line. Often DIY-clearable with a drain snake.
  • Partial blockage in the main line — may clear with snaking, may indicate a structural issue (root intrusion, belly, offset joint).
  • Venting problem — gurgling after flush, or slow drains throughout the house, often indicates a venting issue rather than a clog.

Drain Line Material

ABS — Black plastic, common in homes built from the 1970s onward. Durable, long-lived. Check for joints that have separated or show signs of leaking (staining, mineral deposits, mold growth nearby).

PVC — White plastic, also durable and common in newer construction and remodels.

Cast iron — Found in older homes. Extremely durable but eventually rusts through from the inside. Corrosion shows as orange/rust-colored staining below joints, or visible flaking at the pipe surface. Cast iron in good condition can last 100 years; cast iron in poor condition fails catastrophically.

Orangeburg — Tar paper pipe used in some mid-century construction. Has a documented failure pattern: it absorbs moisture, deforms, and collapses. Found primarily in drain laterals (the underground line from house to sewer). If you have Orangeburg, it's a matter of when it fails, not if. A sewer scope will reveal this.

Sewer Lateral

The drain line connecting your house to the municipal sewer or septic system is not visible to a standard home inspector. A sewer scope inspection (camera fed through a cleanout) is a separate service, typically $150–$350, and is strongly recommended when:

  • The house is more than 30 years old
  • There are large trees near the drain path (roots are the most common cause of blockage)
  • You're buying the property and can't establish history
  • The inspection flagged slow drains throughout the house

What a scope reveals:

  • Root intrusion (most common issue in older neighborhoods with mature trees)
  • Pipe belly (a low point where water pools and debris accumulates)
  • Offset joints (tree roots, soil movement, or settling can shift joints out of alignment)
  • Pipe material (especially relevant for Orangeburg detection)
  • Active blockage

A sewer scope is one of the highest-value optional inspections available on a home purchase. Sewer lateral repair or replacement runs $3,000–$15,000 depending on depth, length, and access. A $300 scope can reveal a $10,000 problem before it becomes your problem.

Venting

The vent system allows air into the drain system so water flows freely rather than creating suction. Vent pipes run up through the wall cavities and exit through the roof.

Signs of venting problems:

  • Gurgling sounds after flushing or draining — water flowing through a drain creates a siphon effect that draws air through the trap if venting is inadequate. You'll hear it.
  • Multiple slow drains simultaneously — individual slow drains are usually clogs; multiple slow drains at once often indicate venting.
  • Sewer gas odor — dried traps (in rarely-used fixtures) or a cracked vent pipe.

What to check:

  • Roof vent pipe penetrations: are they flashed properly? Vent boots (the rubber/lead flashing around the pipe where it exits the roof) are one of the most common sources of roof leaks. Check for cracked rubber, separated flashing, or rust.
  • Are there enough vents? Older homes sometimes have undersized or missing vent branches — a common finding in older houses that have had plumbing modified over the decades without proper permitting.

P-Traps

Every drain has a P-trap — the curved section of pipe that holds water and blocks sewer gas from entering the home. Traps can dry out (in rarely used fixtures), clog, or leak.

What to check:

  • Open the cabinet under every sink and inspect the P-trap. Look for:
    • Active drips or staining (wet cabinet floor, white mineral deposits on the trap)
    • Improper installation — traps shouldn't run uphill or have multiple bends stacked
    • Plastic traps with rubber slip-joint connections: look for compression fittings that have loosened over time
  • For floor drains: pour water into them periodically to keep the trap wet. A dry floor drain trap lets sewer gas into the house.

Cleanouts

Cleanouts are access points in the drain system for snaking and inspection. They're usually 3- or 4-inch plastic or cast iron caps flush with the floor or at a T-junction in a drain line.

What to check:

  • Is there a main cleanout accessible in the basement or exterior? This is where a drain snake or sewer camera is inserted.
  • Are cleanout caps present and not cracked? A missing or damaged cleanout cap can let sewer gas into the space.

Section 3: Water Heater

Water heaters are the most commonly inspected and flagged item in a plumbing inspection. They have a defined service life, visible failure modes, and safety devices that must be functional.

Age and Expected Lifespan

Tank water heaters — Standard lifespan is 8–12 years. The manufacture date is on the label (usually a date code in the serial number — look it up for the specific brand). A water heater over 10 years old is a deferred maintenance item in any inspection report.

Tankless water heaters — Lifespan 15–20 years with maintenance. Require annual descaling in hard water areas.

Heat pump water heaters — Newer technology, lifespan 10–15 years with good maintenance.

Temperature and Pressure Relief Valve (T&P Valve)

The T&P valve is the most important safety device on a tank water heater. It opens automatically if temperature exceeds 210°F or pressure exceeds 150 PSI, preventing the tank from becoming a pressure vessel that can rupture catastrophically.

What to check:

  • Is the T&P valve present? Every tank water heater must have one.
  • Is the discharge pipe properly installed? The discharge pipe must:
    • Run downward to within 6 inches of the floor or to a drain
    • Terminate with an air gap (not threaded into a drain)
    • Be the same diameter as the valve outlet
    • Not be capped or blocked (a capped T&P discharge is a safety violation — if the valve opens, pressure has nowhere to go)
  • Is there a drain pan under the water heater, and does it drain somewhere? If the tank develops a slow leak, the pan prevents water damage. Pan without a drain just delays the problem.

Red flag: A capped T&P discharge pipe, a missing T&P valve, or a T&P valve that appears to have been leaking (white mineral deposits or rust on the discharge pipe) — a dripping T&P valve means the tank is operating at excessive temperature or pressure, or the valve itself has failed.

Flue and Combustion (Gas Water Heaters)

What to check:

  • Flue pipe connections: are they properly secured and sloped upward toward the chimney or exterior vent?
  • Backdrafting: hold a lighter near the draft hood at the top of the water heater while it's running. The flame should be pulled inward (toward the flue), not pushed outward. Flame pushed outward indicates combustion gases are spilling into the room — a carbon monoxide hazard.
  • Combustion air: the water heater needs adequate combustion air. In a tightly sealed utility closet without louvered doors or vents, combustion can be starved.

Anode Rod

The sacrificial anode rod inside a tank water heater corrodes preferentially, protecting the tank lining from corrosion. When the anode is consumed, the tank corrodes. Anode replacement (every 3–5 years) dramatically extends tank life.

Most homeowners never replace the anode rod. In a general inspection, you won't see it — but you can ask about it and plan for replacement if the water heater is 4+ years old.

Sediment

In hard water areas, mineral deposits settle at the bottom of the tank. Rumbling or popping sounds during heating indicate sediment buildup. Annual flushing removes sediment and extends tank life. A water heater that's never been flushed and is 8+ years old likely has significant sediment accumulation.

Section 4: Fixtures

Toilets

What to check:

  • Flush function — Complete clearing on a single flush? Weak flush or incomplete clearing indicates a clog, low water level in the tank, or a worn flapper.
  • Fill function — Does the tank refill completely and stop? A toilet that runs intermittently (phantom flush) has a leaky flapper. A toilet that runs continuously has a fill valve issue. Both waste water and add to your bill.
  • Rocking — Grab the toilet at the bowl and apply lateral pressure. Any movement indicates loose bolts or a failed wax ring. A compromised wax ring leaks sewage water under the floor with every flush.
  • Cracks — Inspect the porcelain at the base and tank. A cracked tank is a slow leak waiting to happen.
  • Shutoff valve — Does it operate? See above.

Water dye test for silent leaks: Put food coloring in the tank. Wait 15 minutes without flushing. If color appears in the bowl, you have a leaking flapper. Silent toilet leaks waste 30–500 gallons per day.

Sinks and Faucets

What to check:

  • Hot and cold function at each faucet
  • Drip at spout (worn cartridge or O-ring) — even a slow drip wastes hundreds of gallons per month
  • Aerator condition — mineral buildup in the aerator restricts flow and is easy to clean or replace
  • Supply lines under the sink — flexible braided supply lines have a manufacturer-recommended replacement interval (typically 5 years for rubber-core, longer for stainless braided). Look for kinks, staining, or swelling at the fittings.
  • Cabinet interior — staining, swelling of the cabinet floor, mold smell. These indicate a past or current leak.

Showers and Tubs

What to check:

  • Caulk at the tub/shower surround — Failed caulk at the tub lip or shower pan is the most common entry point for water into framing and subfloor. Look for caulk that's separating, cracked, or missing.
  • Grout in tile surrounds — Missing or cracked grout allows water penetration. In a tiled shower, run your hand along the grout lines. Soft or hollow-sounding tile indicates water has already gotten behind.
  • Shower pan liner — Older showers have lead or vinyl pan liners. A leak test (plug the drain, fill to the weep holes, wait 24 hours) is the definitive test for pan liner integrity. A failed pan liner means water is running into the subfloor every time someone showers.
  • Showerhead flow — Low flow often indicates mineral buildup at the showerhead or flow restrictor. Usually a maintenance item, not structural.
  • Diverter — The diverter (tub spout to showerhead switch) should route flow completely. If water continues to come from the tub spout when the shower is on, the diverter is worn.

Kitchen

What to check:

  • Under-sink cabinet: supply lines, P-trap, and drain connections. Water staining on the cabinet floor indicates a past or ongoing leak.
  • Dishwasher connection: inspect the supply line and drain hose behind the dishwasher (if accessible). The drain hose should have a high-loop or air gap to prevent backflow.
  • Garbage disposal: run it and listen. Humming without grinding usually means a jam (use the hex wrench at the bottom to free it). Check under the sink for leaks at the disposal flange — this is a common failure point after disposal replacement.
  • Refrigerator ice maker line: if connected, inspect the supply line. Plastic saddle valves (common DIY installs) are notoriously unreliable and should be replaced with proper compression fittings.

Section 5: Sump Pump

If the house has a basement or crawl space, there's likely a sump pump. The sump pump is the last line of defense against water intrusion — and it's only as good as its last test.

What to Check

Primary pump function:

  • Pour a 5-gallon bucket of water into the sump pit slowly. The pump should activate when the water reaches the float trigger and clear the pit completely.
  • Listen for smooth operation — grinding or rattling indicates a problem.
  • Confirm the discharge pipe is connected and routed away from the house (at least 10 feet, sloped consistently downhill).

Check valve:

  • There should be a check valve on the discharge pipe above the pump to prevent water from draining back into the pit when the pump stops. Without it, the pump cycles repeatedly as water returns.

Backup power:

  • Sump pumps fail when you need them most — during heavy storms that also knock out power. A battery backup system or water-powered backup pump is worth having. Note whether one is present.

Secondary/battery backup:

  • Test separately if present.

Float switch:

  • The float should move freely. A float that's stuck against the pit wall won't trigger the pump.

Discharge line routing:

  • As covered in the foundation section: discharge within 5 feet of the house often recirculates water back to the pit. Extend the line.

Pit Condition

  • Is there standing water in the pit between rain events? Some water is normal; a pit that's constantly full suggests inadequate pump capacity, continuous groundwater intrusion, or a failed pump.
  • Is the pit covered? An open sump pit allows radon gas and moisture vapor to enter the living space.
  • Is there debris in the pit? Gravel and sediment accumulation can jam the pump.

Section 6: Outdoor Plumbing

Hose Bibs

What to check:

  • Do they operate and shut off fully?
  • Is a vacuum breaker (backflow preventer) present? This prevents contaminated outdoor water from siphoning back into the supply. Required by code in most jurisdictions.
  • Freeze damage: in cold climates, hose bibs should be frost-free (the shutoff is inside the wall, not at the exterior). A non-frost-free hose bib that wasn't disconnected before a hard freeze may have a cracked stem.

Irrigation Systems

Irrigation systems have their own set of inspection points:

  • Backflow preventer: present and tested? Most jurisdictions require annual backflow testing on irrigation systems.
  • Control valve operation: do zone valves open and close fully?
  • Head condition: broken or misaligned heads waste water and can undermine grade near the foundation.
  • Controller: is the schedule current? Irrigation running in winter is a sign no one has maintained the system.

Exterior Drains and Area Drains

  • Are area drains clear and flowing?
  • Do they connect to a proper drainage destination (daylight or storm system) and not to the sanitary sewer? In many jurisdictions, connecting surface drainage to the sanitary system is a code violation.

Section 7: Water Quality

A plumbing inspection covers the physical system. Water quality is a separate assessment, but worth noting:

Hard water indicators:

  • White mineral deposits at faucet aerators, showerheads, and toilet rim holes
  • Spots on glass shower doors that don't clean off
  • Shortened appliance life (water heaters, dishwashers, washing machines)

Hard water causes scale buildup in pipes and appliances over time. A water softener addresses this. If you're in a hard water area and there's no softener, factor in more frequent appliance maintenance.

Well water systems: If the home is on a well rather than municipal supply:

  • When was the well last tested? Annual testing for coliform bacteria is recommended; every 3–5 years for a broader panel (nitrates, heavy metals, pH).
  • What is the static water level? Very low static level during a drought year can indicate a marginal well.
  • Pressure tank condition: waterlogged pressure tanks (where the bladder has failed) cause the pump to cycle rapidly on and off ("short cycling"), which dramatically shortens pump life.
  • Well pump age: submersible pumps typically last 15–25 years. If the pump age is unknown on a house with a well, budget for potential replacement.

The Pre-Listing Plumbing Check: What Sellers Should Do

If you're selling, a buyer's inspector is going to walk through everything above. Here's what to address before listing to avoid negotiation leverage on the other side:

Item DIY? Cost if deferred
Slow drains Yes — snake or drain cleaner Negotiation leverage
Running toilets Yes — flapper or fill valve ($15–$30 in parts) Water bill + negotiation
Dripping faucets Yes — cartridge replacement Negotiation
Caulk at tub/shower Yes — $10 in materials, 1 hour Mold damage if left longer
Water heater over 10 years Hire out — $800–$1,800 Major negotiation item
Main shutoff valve seized Hire out — $200–$400 Liability
Galvanized pipe Hire out — $2,000–$8,000 depending on scope Major negotiation item
Sump pump test DIY — 5 gallons of water $200–$600 for replacement

The Pre-Purchase Plumbing Check: What Buyers Should Do

In addition to the standard home inspection, buyers should:

  1. Always get a sewer scope on any home older than 30 years, any home with mature trees, or any home where the inspector flagged slow drains. $150–$350 is cheap compared to a sewer lateral replacement.
  2. Note the water heater age and factor replacement into your budget if it's 8+ years old.
  3. Ask about the supply line material — galvanized or polybutylene is a disclosure item and a material cost to factor in.
  4. Test the sump pump yourself during inspection. Don't just take the inspector's word on it — pour water in the pit and watch it respond.
  5. Check every shutoff valve — turn them and confirm they move. If they don't, that's an immediate replacement.

Maintenance Intervals: What to Do and When

Task Frequency DIY?
Flush water heater (drain sediment) Annually Yes
Test T&P valve (lift lever briefly) Annually Yes
Replace anode rod Every 3–5 years Yes (if accessible)
Exercise all shutoff valves Annually Yes
Test sump pump Every 6 months Yes
Inspect supply lines under sinks Annually Yes
Re-caulk tub/shower Every 3–5 years Yes
Backflow preventer test (irrigation) Annually Hire out
Sewer scope Every 5–10 years (older homes) Hire out
Water pressure test Annually Yes ($10 gauge)
Well water test Annually (bacteria) / Every 3–5 years (full panel) Hire out

When to Call a Plumber vs. DIY

DIY:

  • Replacing a toilet flapper or fill valve
  • Cleaning or replacing an aerator
  • Snaking a slow sink or tub drain
  • Re-caulking a tub or shower surround
  • Replacing a showerhead
  • Extending a sump pump discharge line
  • Replacing supply lines under a sink (braided flexible lines)
  • Flushing a water heater

Call a plumber:

  • Any work involving the main line or shutoff
  • Water heater replacement
  • Supply line material replacement (galvanized, PB)
  • Sewer lateral repair or replacement
  • Anything behind a wall
  • Low water pressure diagnosis (could be supply side, PRV, or main line)
  • Sump pump replacement
  • Any leak you can't trace to a visible fitting

What the Inspection Report Means

Inspection reports use phrases like "recommend further evaluation," "deferred maintenance," and "not functional." Here's what they actually mean in terms of urgency:

Safety hazard — Requires immediate attention. Examples: capped T&P discharge, active gas leak at water heater, cross-connection (non-potable water back-feeding supply).

Recommend repair — Should be addressed before closing or factored into offer price. Examples: running toilet, seized shutoff valve, water heater over useful life, cracked supply line.

Monitor — Not urgent but worth watching. Examples: slow drain that cleared during inspection, minor mineral buildup, older water heater within useful life.

Further evaluation recommended — The inspector found something that warrants a specialist. This usually means a plumber or sewer scope company should take a look before you close.

The Short Version

A plumbing inspection is a systematic check of:

  1. Supply — pressure, material, shutoffs, main valve
  2. Drain — flow, material, venting, sewer lateral (scope separately)
  3. Water heater — age, T&P valve, flue, sediment
  4. Fixtures — function, leaks, caulk, supply lines
  5. Sump pump — function, discharge routing, backup power
  6. Outdoor — hose bibs, irrigation, area drains

Most plumbing problems are findable before they become expensive. The ones that become expensive are the ones nobody looked at.