How to Check Plumbing When Buying a House

Most homebuyers spend hours choosing paint colors and minutes thinking about plumbing — until a burst pipe or a $7,000 sewer repair teaches them otherwise. Learning how to check plumbing when buying a house is one of the highest-value skills in real estate, because the plumbing system is hidden, expensive to fix, and easy to overlook during a showing. This guide walks you through a practical, step-by-step plumbing check you can do yourself during showings and the professional inspection, so you buy with your eyes open and negotiate from facts instead of hope.

Start With the Basics: Water Pressure and Color

Your first plumbing test takes thirty seconds and needs no tools. At the kitchen sink, turn on the cold water full blast. It should come out strong and steady. Now turn on the hot water. Then flush a toilet while the tap is running, and turn on the shower. If the kitchen tap slows to a trickle when other fixtures run, the supply system is restricted or undersized — a common problem in older homes with corroded galvanized pipes.

Normal residential water pressure is 40 to 80 psi. You can measure it precisely with a $10 pressure gauge that screws onto an exterior hose bib, and it is worth doing during the inspection. Below 40 psi, showers feel weak and modern fixtures underperform. Above 80 psi, the system is overstressed and needs a pressure-reducing valve. Ask your inspector to record the pressure reading in the report — it is a number you can compare against the standard, not a vague impression.

Water color matters just as much. Fill a white cup or a clear glass from the kitchen tap first thing in the morning, or after the water has sat for a few hours. It should be clear. Brown, yellow, or rusty water means corrosion inside the pipes, usually galvanized steel shedding rust. Blue or green tint can indicate copper corrosion. Cloudy water that clears from the bottom up is usually just air bubbles and is harmless; cloudy water that stays cloudy may indicate sediment or a well problem. If the water is discolored, note it and ask the inspector to investigate — and consider a $50 to $150 water test for lead and metals before closing.

Check Every Fixture, One by One

During the showing or the inspection, run every fixture in the house. This sounds tedious, but it takes ten minutes and catches problems that a quick glance never will. Turn on every faucet, flush every toilet, run every shower, and start the dishwasher and washing machine if the seller allows it.

At each faucet, check three things: does the water run clear, does it reach full pressure quickly, and does it switch cleanly between hot and cold? A faucet that sputters may have air in the lines or a failing cartridge. A faucet that only delivers lukewarm water may have a crossed connection or a water heater problem. Handles that are stiff, loose, or dripping need repair — cheap individually, but a house full of worn fixtures adds up to $500 or more.

Flush every toilet and watch it refill. A toilet that runs constantly wastes hundreds of gallons a month and usually needs a $10 flapper — but a toilet that rocks when you sit on it signals a failed wax ring and possibly a rotted subfloor, a $500 to $2,000 repair. Check the base of each toilet for staining or soft flooring. Look for water stains on the ceiling below any upstairs bathroom.

Run every shower and check the drain. A shower that fills up while you stand in it has a partial clog or a venting problem. Test the shower temperature: it should get properly hot within a minute. If it stays lukewarm, the water heater may be undersized, failing, or set too low. Check that the tub or shower diverter works and that the showerhead does not leak at the connection.

Look Under Sinks and Around Toilets

The space under a sink tells you more about a home's plumbing health than almost anywhere else. Open every cabinet, shine your phone flashlight inside, and look for water stains, warped wood, mold, or a musty smell. Active drips are obvious; dried mineral deposits and green corrosion on trap fittings are the quiet signs of a leak that has been going on for months.

Check the trap under each sink. It should be a P-trap — a U-shaped bend that holds water to block sewer gas. S-traps, which curve straight down without a proper vent, siphon dry and let gas into the home; they are a common defect in older and DIY plumbing. Look for mismatched materials, such as a plastic trap connected to a steel drain with a rubber boot — not necessarily wrong, but worth noting if it looks like a hurried repair.

Around toilets, press the floor gently with your foot near the base. Soft or spongy flooring means the subfloor has been damaged by a long-term wax ring leak. Look for discoloration or swelling in the baseboards behind the toilet. In the basement or crawlspace, look up at the subfloor beneath bathrooms for stains, mold, or repairs.

Find Out What the Pipes Are Made Of

Pipe material is the most important plumbing fact about a home, and it is easy to check. Look at the pipes where they enter the house (near the water meter), at the water heater connections, and in the basement or crawlspace if accessible. Copper is smooth and reddish-brown. PEX is flexible plastic, usually red for hot and blue for cold. CPVC is cream-colored rigid plastic. Galvanized steel is dull gray with threaded fittings. Polybutylene is gray or blue plastic, often stamped "PB2110".

Galvanized and polybutylene supply pipes are the two big red flags. Galvanized pipes rust from the inside and last 40 to 50 years, so any home still running on them in 2026 needs a repipe budgeted at $4,500 to $12,000. Polybutylene reacts with chlorine and fails suddenly; many insurers refuse to cover homes that have it, and replacement runs $4,000 to $10,000. Our galvanized pipes inspection guide and our polybutylene pipe problems guide explain both materials in detail.

Mixed materials are common in older homes that have been partially repiped. A house with copper at the water heater and galvanized everywhere else has not been repiped — it has been patched. Ask the seller for repipe permits and invoices. A permitted, documented repipe adds value; an undocumented partial repipe is a question mark.

Test the Drains and the Sewer Line

Drains are easy to test and easy to ignore. Fill each sink halfway and let it drain — it should empty quickly and quietly. Slow draining in one fixture usually means a local clog. Slow draining in several fixtures at once points to a main line problem. Gurgling sounds, water backing up into a tub when a toilet flushes, or sewage odors all suggest a partial blockage or a venting defect.

The sewer line is the most expensive plumbing component in a home, and a standard home inspection does not include it. The line runs underground from the house to the street, and inspectors cannot see inside it. That is why a sewer scope — a camera inspection of the main line — is the single most valuable add-on inspection you can order, at $200 to $450 in 2026. The camera reveals cracks, root intrusion, collapsed sections, and bellies (low spots where waste collects). Replacement costs run $3,000 to $7,000 for a straightforward run and up to $15,000 under a driveway. Our drain camera inspection cost guide explains exactly what the camera shows.

Order a sewer scope on any home older than 25 years, any home with large trees near the sewer line, and any home where the inspection found slow drains, gurgling, or odors. If the seller refuses access for a scope, treat that as a red flag in itself. In competitive markets, some buyers waive the sewer scope to win the bid — a $300 saving that has cost many buyers $5,000 after closing.

Also find the main sewer cleanout, usually a capped pipe near the house foundation or in the yard. A home with no accessible cleanout makes every future drain job more expensive, because the plumber has to pull a toilet to access the line. Note its location for your own reference — you will need it someday.

Inspect the Water Heater

The water heater is the hardest-working appliance in the house, and it is easy to evaluate. Find the rating plate on the tank — it lists the manufacture date, capacity, and model. Standard tank heaters last 8 to 12 years; tankless units last 15 to 20 years. A heater older than 10 years is a near-term replacement cost of $1,200 to $3,500, and that should factor into your offer.

Look for rust or corrosion on the tank, the pipe connections, and the burner area. Check for water pooling at the base, which indicates a tank leak — a heater that is leaking from the tank itself cannot be repaired and must be replaced. Check the temperature and pressure (T&P) relief valve discharge pipe: it should run downward and end 6 inches above the floor or drain outside, never into a wall cavity. A missing or improperly routed T&P line is a safety defect.

On gas heaters, check the venting. The flue should rise steadily to the chimney or vent, with no sagging sections, and there should be no scorch marks or melted plastic near the draft hood, which indicate backdrafting — exhaust gases spilling into the home instead of going up the flue. If the heater sits in a garage, it should be elevated 18 inches off the floor in most jurisdictions. In earthquake-prone areas, check for seismic strapping.

If the heater is in a finished area, look for a drain pan underneath, piped to a drain. A pan costs little and prevents a tank failure from flooding the floor below. Its absence is a minor flag, but a cheap one to fix after closing.

Read the Disclosures and Permit History

The seller's disclosure and the local permit history are free sources of plumbing information that many buyers skip. Read them carefully before your inspection contingency expires.

When to Hire a Plumber Before Closing

A general home inspector is a generalist. They are trained to spot problems across every system in the house, but they are not plumbers, and they do not price repairs. Bring in a licensed plumber when any of the following show up:

• Galvanized or polybutylene pipes are confirmed. Get a written repipe estimate. It becomes your negotiating leverage and your budget.
• Multiple drains are slow or gurgling. A plumber can run a camera and tell you whether it is a $300 snaking or a $5,000 line replacement.
• Water pressure is low throughout the house. A plumber can determine whether the cause is the pressure regulator, the main line, or internal corrosion — three very different price tags.
• The water heater shows rust, leaks, or venting problems. A plumber can confirm whether it needs replacement now or has a few years left.
• There are active leaks inside walls or ceilings. A plumber can open the wall, find the source, and quote the repair — including drywall and paint.
• The sewer scope found damage. Get a written repair estimate with the camera footage referenced, so you can negotiate a specific dollar amount.

A plumber's pre-purchase evaluation typically costs $150 to $350 and takes about an hour. Schedule it during your inspection contingency window, and ask for everything in writing with photos. Those written estimates are the most powerful tool in your negotiation: a seller can dismiss an inspector's note, but a plumber's $8,000 repipe quote is a number that has to be answered. For a complete checklist of everything an inspector examines, start with our plumbing inspection checklist and the home inspection hub before your contingency clock runs out.