20 Plumbing Systems Practice Questions & Answers

1. 1. A house is served by a drilled well with a pressure tank in the basement. Within the scope of a general home inspection, how should the inspector handle the water supply?

   • A.Collect a water sample, have it tested for bacteria, and include the laboratory results in the plumbing section of the report
   • B.Remove the cover from the pressure tank controls and adjust them until the pump cycles correctly
   • C.Describe the supply as private, report the visible condition of the accessible piping and equipment, and explain that the well, the pump and water quality are outside the scope of the inspection✓ Answer
   • D.Measure the well's yield and state in the report whether it is adequate for the size of the household

   A general home inspection is visual and non-invasive. The inspector is expected to describe whether the water supply is public or private and to report the observable condition of accessible components, but wells, pumps and water-quality testing are excluded from the inspection, so the correct handling is to describe, report what is visible, and disclose the limitation.

   Source: Home inspection standards of practice — plumbing: items inspected, limitations and exclusionsReport a problem with this question

2. 2. Flow at an upstairs bathroom located farthest from the water entry is noticeably weak, while flow at the fixture nearest the entry remains strong. The visible supply piping is threaded galvanized steel of considerable age. Which mechanism best explains this pattern?

   • A.Air trapped at the high point of the system permanently blocks the branch serving the most distant fixture
   • B.The zinc coating flakes off the outside of the pipe, thinning the wall so that pressure bleeds away before it reaches distant fixtures
   • C.Galvanized steel expands as it heats, and the expansion progressively closes the pipe at the end of the longest run
   • D.Rust and mineral scale build up on the inside wall of the pipe, and because the restriction accumulates over every foot of pipe travelled, the fixture farthest from the water entry loses flow first✓ Answer

   Galvanized steel piping corrodes from the inside as the protective zinc is lost, and the resulting rust nodules and scale (tuberculation) narrow the bore. Because each length of pipe adds restriction, the loss of flow is cumulative along the run, which is why the fixture at the end of the longest path shows the symptom first.

   Source: National Home Inspector Examination content outline — plumbing systems: water supply distribution materials and typical defectsReport a problem with this question

3. 3. In a copper water distribution system the inspector finds repeated pinhole leaks and thin spots on the outside of elbows immediately downstream of a partly closed valve, with blue-green staining below them. Which mechanism is the best explanation?

   • A.Erosion corrosion: high velocity and turbulence strip the protective film from the inside of the tubing, so metal loss concentrates at fittings where the flow changes direction✓ Answer
   • B.Freeze expansion that split the tubing during a previous winter and was patched at the elbows
   • C.Galvanic corrosion caused by contact between the copper and a dissimilar metal at those fittings
   • D.Ultraviolet degradation of the copper wall where the tubing is exposed

   Copper relies on a thin protective film on its inner surface. Where velocity is high and the flow is turbulent — at elbows, at fittings, and downstream of a restriction — that film is continuously swept away and fresh metal is exposed, so wall loss and pinholes cluster at those points rather than randomly along straight runs.

   Source: National Home Inspector Examination content outline — plumbing systems: copper tubing and its corrosion mechanismsReport a problem with this question

4. 4. A run of PEX water piping crosses an open crawl-space vent and is exposed to direct sunlight for part of each day. Why should the inspector report this condition?

   • A.Ultraviolet light degrades the polymer and embrittles the pipe over time, so PEX is meant to be shielded from sunlight✓ Answer
   • B.Sunlight heats the water inside the pipe beyond what any plastic piping is able to carry
   • C.PEX is not approved to carry hot water under any circumstances, so the entire run must be replaced with copper
   • D.PEX is intended for exterior use only, so it is the portion inside the crawl space that is misapplied

   PEX is rated for both hot and cold potable water, but the polymer is sensitive to ultraviolet exposure: sunlight breaks down the material and the pipe becomes brittle and prone to cracking. Sun-exposed PEX is therefore an observed condition to describe and recommend for correction, whereas the claims about hot water and exterior-only use are false.

   Source: National Home Inspector Examination content outline — plumbing systems: plastic water distribution piping and material limitationsReport a problem with this question

5. 5. In a crawl space the inspector observes flexible grey plastic water supply piping joined with plastic insert fittings and metal crimp rings, a material historically associated with failures at and near the joints. What is the appropriate handling of this observation?

   • A.State conclusively that the piping is polybutylene and that it will fail within five years
   • B.Leave the observation out of the report, because plastic supply piping is not part of a plumbing inspection
   • C.Describe the piping as observed, report it as a condition with a known history of joint failure, and recommend evaluation by a licensed plumber while noting that positive identification of the material is beyond a visual inspection✓ Answer
   • D.Cut out a short sample of the pipe and send it for laboratory identification before completing the report

   The inspection is visual and non-invasive, and standards of practice do not require the inspector to positively identify a supply piping material or to predict when a component will fail. The defensible report describes what was seen, states the implication as a condition, and refers it to the appropriate trade; cutting a sample would be destructive and is outside the scope.

   Source: National Home Inspector Examination content outline — plumbing systems: supply piping materials, and standards of practice on reporting versus destructive investigationReport a problem with this question

6. 6. At a repair, copper tubing has been connected directly to the existing galvanized steel piping. Heavy rust-coloured corrosion has built up at that connection and the joint is weeping. What explains the deterioration, and what interrupts it?

   • A.Two dissimilar metals joined in a wet system form a galvanic cell and the more active metal corrodes rapidly at the joint; a dielectric fitting that separates the two metals interrupts the process✓ Answer
   • B.Water hammer from a fast-closing valve nearby; adding an arrester would stop it
   • C.Erosion corrosion from high velocity; increasing the diameter of the copper at the connection would stop it
   • D.Thermal expansion of the copper; an expansion loop installed at the connection would relieve it

   When copper and galvanized steel are joined and water provides an electrolyte, an electrical potential drives accelerated corrosion of the more active metal at the junction. A dielectric fitting or union breaks the metal-to-metal path so the galvanic cell cannot operate; the inspector reports the corroded, leaking connection and recommends repair.

   Source: National Home Inspector Examination content outline — plumbing systems: joining dissimilar piping materials and galvanic corrosionReport a problem with this question

7. 7. While water is running at a bathroom lavatory, the inspector opens a second fixture and the flow at the lavatory drops noticeably. What is the best way to handle this finding?

   • A.Disregard the observation, because operating two fixtures at once is not a valid inspection method
   • B.Attach a gauge, record the system pressure and state in the report that the water pressure is inadequate for the house
   • C.Report reduced functional flow as an observed condition and recommend evaluation by a licensed plumber, noting that judging the adequacy of water pressure or supply sizing is outside the scope of the inspection✓ Answer
   • D.State in the report that the supply piping is corroded internally and that the house must be repiped

   Running two fixtures simultaneously is the accepted qualitative check of functional flow, and a noticeable drop points to restriction somewhere in the supply — corrosion, undersized piping, a partly closed valve or a pressure problem. The inspector reports the observed behaviour and its implication, but determining pressure adequacy, flow rates and pipe sizing is expressly excluded from a general inspection.

   Source: Home inspection standards of practice — functional flow testing and the exclusion of pressure, flow and sizing determinationsReport a problem with this question

8. 8. A lavatory that is used every day gives off a persistent sewer odour. Inside the trap the inspector finds a length of rag-like debris hanging over the trap dip and down the outlet leg, and the trap is only partly filled. Which mechanism has emptied the seal?

   • A.Self-siphonage, in which the fixture's own discharge pulls the seal out behind it
   • B.Evaporation of the seal water, which is expected in a fixture used this often
   • C.Capillary action, in which the absorbent material wicks water over the trap dip and out of the trap✓ Answer
   • D.Back pressure, in which positive pressure in the drain blows the seal out of the trap

   A trap seal can be lost by siphonage, back pressure, evaporation or capillary action. Evaporation is ruled out by daily use, and the described absorbent material bridging the dip provides a wick that draws water continuously out of the trap, which is the classic capillary-action case; the remedy is removing the obstruction, and the odour is reported as an active condition.

   Source: National Home Inspector Examination content outline — drain, waste and vent systems: traps and the mechanisms of trap seal lossReport a problem with this question

9. 9. Under a bathroom lavatory the trap outlet turns downward and drops vertically into the floor, and there is no vent connection anywhere on the trap arm. Why is this configuration reportable?

   • A.The vertical drop makes the trap seal deeper than intended, so the fixture drains slowly
   • B.The configuration places the trap below the frost line, so the seal is likely to freeze
   • C.The vertical drop lets a full slug of discharge act like a siphon that pulls the seal water out with it, leaving the trap dry and open to sewer gas✓ Answer
   • D.The configuration forces waste to flow uphill through the trap arm before it reaches the drain

   This is the classic S-trap arrangement. Because the outlet drops straight down with no vent to admit replacement air, the falling column of water creates negative pressure that siphons the seal out behind it, and once the seal is gone sewer gas enters the room. The inspector reports the configuration and recommends correction by a plumber.

   Source: National Home Inspector Examination content outline — drain, waste and vent systems: prohibited trap configurationsReport a problem with this question

10. 10. Which statement best describes the function a vent performs for a fixture trap in a drain, waste and vent system?

    • A.It blocks sewer gas from entering the room, which is the reason a trap by itself is not sufficient
    • B.It supplies combustion air to any fuel-burning appliance sharing the same chase
    • C.It increases the effective slope of the fixture drain so that waste moves away faster
    • D.It admits air behind the water flowing down the drain so pressure stays near atmospheric and the trap seal is neither siphoned out nor blown out✓ Answer

    The trap is what blocks sewer gas; the vent is what protects the trap. A slug of water falling down a drain would otherwise create negative pressure behind it and positive pressure ahead of it, and the vent equalises both by connecting the drain to outside air, which is also why unvented fixtures gurgle and drain sluggishly.

    Source: National Home Inspector Examination content outline — drain, waste and vent systems: venting principlesReport a problem with this question

11. 11. A kitchen sink discharges through a P-trap under the cabinet and then through a second trap in the floor below before reaching the branch drain. The fixture drains sluggishly and gurgles. What should the inspector report?

    • A.The gurgling is caused by trap seals that are deeper than necessary and is corrected by draining one of them
    • B.The arrangement is acceptable, because the second trap gives added protection against sewer gas
    • C.The fixture is double trapped: air caught between the two seals has no way out and resists the flow, so drainage is sluggish; the condition should be reported for correction by a plumber✓ Answer
    • D.The second trap serves as the fixture's vent, so only the missing cleanout needs to be reported

    Double trapping a single fixture is a recognised defect: the pocket of air between the two water seals cannot be displaced or vented, so it air-locks the line and the fixture drains slowly and gurgles. A trap is never a vent, and a fixture is served by one trap unless an approved multi-compartment arrangement applies.

    Source: National Home Inspector Examination content outline — drain, waste and vent systems: double trapping and typical defectsReport a problem with this question

12. 12. Beneath a laundry sink the trap arm is a length of flexible corrugated plastic tubing that sags between the trap and the wall. Why is this a defect worth reporting?

    • A.Flexible tubing lets sewer gas pass directly through its wall into the cabinet
    • B.The corrugations make the inside of the drain too smooth, so waste moves past before the trap can refill
    • C.Corrugated tubing cannot hold a trap seal at all because it is not rigid
    • D.The ridged interior catches solids and cannot be cleaned effectively, and the sag holds standing waste, so the arm blocks progressively✓ Answer

    Corrugated flexible tubing used as drain piping is a recognised defect because the internal ridges trap grease and solids that a cable or brush cannot clear, and unsupported flexible tubing sags into low spots that hold waste. The inspector describes the installation and recommends replacement with smooth, properly sloped and supported piping.

    Source: National Home Inspector Examination content outline — drain, waste and vent systems: typical defects in fixture drains and trap armsReport a problem with this question

13. 13. A garden hose is attached to the laundry-tub faucet and its free end lies in the bottom of the tub. Why is this a cross-connection, and what is the basic protection?

    • A.The hose end sits below the flood-level rim, so a loss of supply pressure could siphon tub contents back into the potable piping; an unobstructed air gap above the rim, or a vacuum breaker at the outlet, prevents that✓ Answer
    • B.It is a cross-connection only while the faucet is running, so no protection is needed once the faucet is closed
    • C.The real risk is that the hose will burst under pressure, and a pressure-reducing valve at the meter is the protection
    • D.It is not a cross-connection, because the laundry tub is trapped and vented

    A cross-connection is any arrangement that could let non-potable water enter the potable supply. A submerged outlet below a fixture's flood-level rim provides exactly that path if supply pressure falls, and the simplest reliable protection is a physical air gap above the rim, with a vacuum breaker used where an air gap is not practical.

    Source: National Home Inspector Examination content outline — plumbing systems: cross-connection control, air gaps and vacuum breakersReport a problem with this question

14. 14. A boiler make-up water line is connected to the potable water supply, and the boiler can operate at a pressure higher than the pressure in the house supply piping. Which statement best describes the hazard?

    • A.Back-siphonage, because the boiler sits at a level above the water meter
    • B.Backpressure, because pressure downstream of the connection can exceed supply pressure and push non-potable water back into the potable piping, unlike back-siphonage, which is caused by negative or reduced pressure in the supply✓ Answer
    • C.Backpressure, which a single check valve at the boiler fully addresses because a heating system is a low-hazard connection
    • D.Back-siphonage, because heated water expands and therefore reverses direction in the supply line

    Backflow occurs by two distinct mechanisms: back-siphonage, driven by negative or reduced pressure on the supply side, and backpressure, driven by a downstream pressure that exceeds supply pressure. A boiler is a backpressure situation and is treated as a hazardous connection needing a listed backflow preventer, not merely a check valve.

    Source: National Home Inspector Examination content outline — plumbing systems: backflow mechanisms, back-siphonage versus backpressureReport a problem with this question

15. 15. At a storage water heater the temperature-and-pressure relief valve discharges into a pipe that first rises above the top of the tank, then turns down, is reduced in diameter at a coupling, passes through a shutoff valve, and ends in a threaded fitting. Which statement best describes the problem?

    • A.The only defect is the threaded end; the rest of the arrangement is acceptable as long as the pipe eventually turns downward
    • B.The arrangement is acceptable, because the shutoff valve lets a plumber isolate the relief valve for servicing
    • C.A relief discharge line must remain full size, contain no valve, run downward so it drains by gravity without traps, and terminate unthreaded where a discharge would be seen; the rising section, the reduction, the valve and the threaded end each defeat that purpose✓ Answer
    • D.The arrangement is acceptable, because reducing the pipe increases the velocity of any discharge and clears it faster

    The discharge line exists so a relieving valve can dump hot water safely and so the discharge is noticed. Anything that can obstruct or hold water — a rise, a trap, a size reduction, a valve — can prevent relief or hide the fact that the valve has operated, and threads at the end invite capping. Each of the observed items is reported as a safety defect for correction.

    Source: National Home Inspector Examination content outline — water heating systems: relief valve discharge piping configurationReport a problem with this question

16. 16. The temperature-and-pressure relief valve on a water heater has no discharge piping at all; its outlet is open at the top of the tank at roughly head height in a finished basement. What is the correct response?

    • A.Note it only if the water heater is also leaking, since the valve itself appears functional
    • B.Lift the valve's test lever to confirm that it opens and reseats, then report the result
    • C.Fit a temporary discharge tube so that the condition is safe for the remainder of the inspection
    • D.Report the missing discharge piping as a safety defect, explain that a discharge at that location could scald anyone standing nearby, and recommend correction by a licensed plumber✓ Answer

    Operating safety valves and making repairs are both outside the scope of a general inspection, and lifting the lever on an old valve can leave it leaking. The inspector's job is to observe, state the safety implication — an unpiped relief outlet can spray scalding water on an occupant — and refer it to the appropriate trade. A discharge line that ends in a concealed space is reported the same way.

    Source: Home inspection standards of practice — water heater relief valves: reporting requirement and the exclusion of operating safety valvesReport a problem with this question

17. 17. After the burner of an atmospherically vented gas water heater has been running for several minutes, the inspector feels warm, moist air at the relief opening of the draft hood and sees smoke drawn outward into the room rather than up the vent. There is rust on the hood and on the top of the tank. What does this indicate?

    • A.Normal operation, because a draft hood is designed to let flue gases spill outward into the room whenever the burner is firing
    • B.Too much combustion air in the room, which is corrected by sealing the openings that supply the space
    • C.The appliance is spilling combustion products into the living space instead of venting them, a safety condition that should be reported at once with a recommendation for prompt evaluation and correction✓ Answer
    • D.An oversized burner orifice, which the inspector should adjust before continuing the inspection

    A draft hood is meant to draw dilution air in, so flow at the relief opening should be inward once the vent is warm. Outward flow of warm, moist flue gas several minutes into a burn is spillage, and the rust confirms it has been happening for some time. Because spilled combustion products can carry carbon monoxide, this is reported immediately as a safety condition, not adjusted by the inspector.

    Source: National Home Inspector Examination content outline — fuel-burning water heaters: draft, venting and spillageReport a problem with this question

18. 18. Which of the following observations at gas-fired appliances is a reportable installation defect?

    • A.A flexible appliance connector that passes through the side wall of a cabinet to reach the appliance✓ Answer
    • B.A clothes dryer gas connection made without a sediment trap
    • C.An appliance shutoff valve located in the same room as the appliance, within reach and upstream of the connector
    • D.A furnace supplied by rigid black steel pipe with a sediment trap installed ahead of the appliance

    A flexible appliance connector is intended to be a single exposed length that can be seen and inspected; running it through a wall, partition, floor or cabinet side hides it and exposes it to chafing at the penetration, so it is a reportable defect. Sediment traps are not expected at every appliance — clothes dryers and ranges are among the usual exceptions — and an accessible shutoff ahead of the connector is correct practice.

    Source: National Home Inspector Examination content outline — fuel distribution: appliance connectors, shutoff valves and sediment trapsReport a problem with this question

19. 19. A water closet rocks when light pressure is applied to the bowl, there is a faint odour near its base, and the flooring immediately around the base is discoloured. What is the best interpretation and report?

    • A.Slight rocking is normal for a fixture set on tile and needs no comment in the report
    • B.The tank bolts are loose; recommend tightening them and note nothing further
    • C.Movement suggests the closet flange, its fasteners, or the floor beneath has deteriorated and that the seal is likely compromised, so waste can escape at each flush; report the condition, note that concealed damage cannot be evaluated visually, and recommend removal and repair by a plumber✓ Answer
    • D.The odour proves the fixture is unvented; recommend that a vent be added to the fixture drain

    A toilet must be rigidly secured to a sound flange. Rocking works the seal loose so a small amount of waste water escapes with every flush, and that water soaks the subfloor, which in turn rots and lets the fixture move more — odour and floor discolouration are the visible evidence of the cycle. The extent of the concealed damage cannot be judged without removing the fixture, which is beyond a visual inspection.

    Source: National Home Inspector Examination content outline — plumbing fixtures: water closet installation defects and related concealed damageReport a problem with this question

20. 20. A brown-edged stain on a living-room ceiling lies directly beneath the second-floor bathroom, and in that bathroom the grout at the base of the shower and the sealant at the tub-to-wall joint are cracked and missing in places. How should the inspector proceed?

    • A.Open the ceiling below to expose the piping and confirm exactly where the leak originates
    • B.Report only that the ceiling is stained, because the possible cause of a stain may not be discussed in an inspection report
    • C.Describe the staining and the failed grout and sealant, explain that water passing through those joints into the wall and floor cavity is a likely source, and recommend evaluation and repair, noting that filling the tub or flood-testing the shower pan is beyond a visual inspection✓ Answer
    • D.Fill the tub to its overflow and flood the shower pan to determine whether the pan leaks before writing the report

    Reporting means describing the observed condition, stating what it implies and directing it to the right trade. Cracked grout and missing sealant at a wet joint are a recognised path for water into the wall and floor cavity, and the stain below is the consequence, so the two observations are linked in the report. Flood-testing a shower pan, filling fixtures to test for leaks and opening finished surfaces are all outside a visual, non-invasive inspection.

    Source: Home inspection standards of practice — moisture staining and reporting, with exclusion of shower pan and fixture flood testingReport a problem with this question

Practice questions based on the National Home Inspector Examination content outline, widely shared home inspection standards of practice, and residential building science. Not affiliated with or endorsed by any examination board, licensing authority, or inspector association. A home inspection is a visual, non-invasive examination and is not a code-compliance inspection — nothing here should be read as a code requirement. Home inspection is regulated differently from place to place; confirm your own jurisdiction's requirements and the standards of practice you are held to before testing or inspecting. About the National Home Inspector Examination →