What does the plumbing inspection cover when buying a house?

The InterNACHI Standards of Practice spell out the plumbing items an inspector checks. The inspector locates the main water shutoff valve so you know where to stop the flow in an emergency. They inspect the water heater, including its energy source, its venting, the temperature and pressure-relief (TPR) valve, and the unit's general condition. The TPR valve matters because it is the safety device that releases pressure before a tank can rupture. The U.S. Department of Energy lists this relief valve and a discharge pipe among the basic safety features every storage water heater should have.

The inspector then tests the interior water supply by running fixtures and faucets, and operates all toilets by flushing them. They check functional drainage at sinks, tubs, and showers, meaning the water clears at a reasonable pace and does not back up while the inspector watches. They inspect the visible parts of the drain-waste-vent (DWV) system, the network of pipes that carries waste out and lets sewer gas escape through roof vents. Where one is present and reachable, they look at the accessible sump pump. Throughout the visit, the inspector reports any visible leaks and checks flow by running two fixtures at once to see whether pressure noticeably drops, a quick way to spot a supply problem.

The flush-and-drain part of the visit is more useful than it sounds. Flushing every toilet catches a running flapper, a weak flush from scaled rim jets, or a wobble at the base that points to a failing wax ring. Running the sinks and tubs while watching the drain reveals slow drainage from buildup in a trap or a venting issue, since a poorly vented drain gurgles and empties slowly. None of this requires opening a wall, which is why it falls inside the inspector's required scope. What it cannot tell you is how the system behaves under a full household load over weeks, only how it behaves for the few minutes water is running.

The InterNACHI standard puts the inspector's basic duty plainly. The inspector "shall inspect" the following: "the main water supply shut-off valve," "the water heating equipment, including the energy source, venting connections, temperature/pressure-relief (TPR) valves, and the operating controls," "the interior water supply, including all fixtures and faucets, by running the water," "all toilets for proper operation by flushing," "all sinks, tubs and showers for functional drainage," and "the drain, waste and vent system." That short list is the backbone of what you are paying for.

A standard inspection has clear limits, and the gaps are where buyers get surprised. The InterNACHI Standards of Practice state the inspector is not required to inspect a long list of items. The biggest ones for a Phoenix buyer:

• Water softeners and water filters. These are treatment appliances, not part of the core plumbing the standard covers.
• Well pumps and onsite water supply. A home on a private well needs its own well and pump evaluation.
• Floor drains, lawn sprinkler systems, and washing-machine connections. All sit outside the required scope.
• Any plumbing behind sealed access panels. If the inspector cannot reach it without taking the house apart, it is not inspected.
• Septic systems and other wastewater-treatment systems. These need a separate specialist, and in Arizona a property sale often triggers a required transfer-of-ownership septic inspection.
• Concealed or underground piping. Anything buried or hidden inside a slab or wall is not part of the visual check.

That last point is the one that costs buyers the most. The sewer line, the buried lateral that runs from the house to the city tap, is concealed underground and is not part of a standard home inspection. To see inside it you need a separate sewer scope, a camera run down the line. InterNACHI treats the sewer scope as an ancillary service that is not part of the Standards of Practice. Because the buyer owns that lateral after closing, a hidden crack, a belly that traps waste, or root intrusion becomes your bill, and a full sewer-line repair is one of the larger plumbing costs a homeowner can face. We cover this in detail in our guide on whether you should get a sewer scope before buying a home.

It is worth knowing why these items sit outside the scope. A home inspector is a generalist who checks the whole house in a few hours. The excluded items either need specialized tools, like a sewer camera, or specialized knowledge, like a well or septic evaluation, or they are simply not reachable without damaging the home. The standard draws the line at what a generalist can fairly judge by sight and operation. That is not a flaw in the inspection; it is the reason the add-on inspections exist.

It helps to understand what kind of test this is. A home inspection is a visual, non-invasive snapshot of the home on one day. The inspector does not turn off the power to test wiring inside a unit, does not open sealed walls, and does not dig. They report the condition they can observe and operate at that moment. The ASHI Standard of Practice describes a home inspection in the same terms, as a non-invasive examination of the readily accessible and visually observable systems of a home.

That means the report is not a warranty or a guarantee. A drain that runs clear during the visit can still hide a partial blockage downstream. A water heater that fires up fine can fail a month later. The inspection lowers your risk by catching obvious and observable problems; it does not promise that nothing will go wrong. It also does not test water quality or pressure against a code standard unless you ask for that as an add-on. Reading the report with this frame keeps your expectations accurate and your negotiations grounded.

Older Phoenix homes raise the stakes, because some of the materials a visual check cannot fully judge, like aging cast-iron drains or polybutylene supply lines, are exactly the ones that fail. Our page on common plumbing problems in older Phoenix homes walks through the pipe materials and eras worth watching.

Because the standard inspection stops at the surface, many buyers add a focused inspection where the risk is highest. The most common add-on for plumbing is the sewer scope, especially on any home built before the 1980s, on a lot with mature trees near the line, or where the seller mentions past backups. A home on a private well should get a dedicated well and pump test. A home on septic needs a septic inspection, which in Arizona is commonly tied to the required transfer-of-ownership filing. If the water heater is near the end of its life or the report flags the TPR valve, a plumber can confirm whether it needs replacement now or soon. To gauge how much life is left, see our guide on how to tell the age and condition of home plumbing.

Use the report as a negotiating tool, not a verdict. Read the plumbing section closely, separate cosmetic notes from real defects, and price out the items the inspector flagged. Visible leaks are worth taking seriously: the EPA notes that household leaks waste nearly 1 trillion gallons of water nationwide every year, and the average home loses more than 9,300 gallons annually to leaks, so a small drip on the report can point to a habit of deferred upkeep. You can ask the seller to repair flagged items, credit you at closing, or adjust the price. If a defect is big or unclear, bring in a licensed plumber for a second opinion before your inspection period ends.

Pay close attention to wording in the report. Inspectors often use careful phrases like "recommend further evaluation" or "at or near the end of expected service life." Those are signals to dig deeper, not throwaway lines. A water heater flagged this way may have years left or may be on borrowed time, and only a closer look settles it. Treat each flagged item as a question to answer during your inspection period, while you can still act on what you learn.

HQ Plumbing & Air serves buyers across metro Phoenix and can run a sewer scope or confirm a flagged plumbing item before your contingency window closes. A standard inspection tells you what is visible; a focused follow-up tells you what is buried.