The pipes carrying water through a home are easy to ignore until they fail, and each material that has been used in residential plumbing has its own story about why it was chosen, how it ages, and what kind of failure to expect from it. Knowing the difference between galvanized steel, copper, PEX, and PVC isn’t just academic. It shapes how a homeowner reads the plumbing they already have, and it informs the choice of replacement material when something needs to be repiped.
Each material has a generation it dominated, a strength that recommended it, and a weakness that eventually caught up with it. Reading those four materials in the order they entered residential plumbing tells most of the story.
Galvanized steel: the long-running standard that aged out
Galvanized steel was the standard supply pipe material in residential construction through much of the early and mid-twentieth century. Steel pipes coated with a layer of zinc to resist corrosion offered a durable, code-accepted, gas-tight option that could be threaded and joined with available tools. Galvanized steel served well for decades, but its long-term failure mode is now well understood.
The zinc coating wears thin from inside the pipe over time, and once exposed steel is in contact with water, corrosion accumulates on the inner walls, narrowing the working diameter and producing rust-colored water at the tap. Older galvanized pipes can also be a source of lead contamination, because the galvanizing process historically used zinc that contained trace lead and because lead solder was sometimes used at fittings. Homes with galvanized supply lines that have been in service for decades commonly produce water with elevated lead and iron levels, and the pipes themselves clog progressively as corrosion accumulates. Most galvanized supply lines installed before the second half of the twentieth century are now at or beyond the end of their useful service life.
Copper: the gold standard, with one weakness
Copper has been the dominant supply pipe material in residential construction since galvanized fell out of favor, and it remains a solid choice in most new and replacement installations. Type L and Type M copper, distinguished by wall thickness, handle the supply pressures and temperatures of residential systems reliably. Properly installed copper supply lines routinely last 50 years or more, with some installations pushing well beyond that depending on water chemistry.
The weakness of copper is acidic water. Water with low pH and high oxygen content corrodes copper from the inside, producing pinhole leaks that can develop quickly once the process is established. Aggressive water chemistry is a regional issue rather than a universal one, and homes in areas with naturally acidic water sometimes see copper failure decades earlier than the material’s nominal lifespan would suggest. Copper is also expensive to install, both in material cost and in labor, and the price has discouraged its use in some new construction in favor of plastic alternatives.
PEX: flexible, freeze-resistant, dominant in new repipes
PEX, or cross-linked polyethylene, has displaced copper in many new installations over the last two decades and has become the dominant material for residential supply line repipes. PEX is flexible, which means it can be run in long continuous pieces with fewer fittings, reducing both installation time and the number of joints that could potentially leak. It tolerates a wider range of water chemistries than copper, resisting both acidic and alkaline water without significant degradation. It expands when water inside it freezes, which gives it a degree of freeze-resistance that rigid pipes lack.
PEX lifespan estimates run roughly 40 to 50 years, which puts it in the same general range as galvanized at its best but without the corrosion failure mode. The limits of PEX are mostly about installation environment: PEX cannot be installed in direct sunlight or in areas with prolonged UV exposure, because UV degrades the material; some early PEX formulations also had issues with chlorinated water that newer formulations have largely resolved. Code acceptance for PEX in residential supply systems is now widespread, though some older jurisdictions retain restrictions worth checking against local code.
PVC and CPVC: drainage standard and hot-water variant
PVC, or polyvinyl chloride, and its variant CPVC, chlorinated polyvinyl chloride, occupy different roles. PVC is the standard material for residential drain, waste, and vent systems in most modern construction, where its corrosion resistance, low cost, and ease of installation make it well-suited to non-pressurized lines carrying wastewater. PVC handles a typical residential drain system for 25 to 40 years or more, and most failures come from physical damage, joint separation, or extreme temperature exposure rather than gradual material breakdown. PVC is generally not used for hot water supply lines because it loses strength at elevated temperatures.
CPVC, which is chemically modified to handle higher temperatures, can be used for both hot and cold water supply, and CPVC supply systems have a useful lifespan in the range of 50 years. CPVC is more brittle than PEX and is more demanding in installation, which has limited its adoption compared to PEX in new repipes, though it remains code-accepted in most jurisdictions.
A side-by-side comparison
| Material | Typical lifespan | Best for | Main weakness |
|---|---|---|---|
| Galvanized steel | 50 to 70 years (legacy installations) | Out of favor; legacy only | Internal corrosion; lead contamination risk |
| Copper | 50+ years | Supply lines in neutral water chemistry | Pinhole leaks in acidic water; high install cost |
| PEX | 40 to 50 years | Most modern supply repipes | UV degradation if exposed; chlorine sensitivity in older formulations |
| PVC | 25 to 40+ years | Drain, waste, and vent systems | Loses strength at high temperature; not for hot supply |
| CPVC | ~50 years | Both hot and cold supply | More brittle than PEX; demanding install |
Choosing for a new installation or repipe
Choosing among these materials in a new installation or a repipe project is mostly about matching the material to the application and the regional water chemistry. Drainage and venting are PVC almost universally. Supply lines in regions with neutral water chemistry can be copper or PEX, with PEX usually winning on installation cost and freeze resistance and copper on longevity in clean water. Supply lines in regions with aggressive water chemistry tilt toward PEX or CPVC because both materials handle a wider chemistry range than copper. Supply lines in older homes that still have galvanized are repipe candidates rather than repair candidates, because the galvanized failure mode is systemic rather than localized. Whole-house repipe decisions and the conditions that justify them are covered in a dedicated guide on repipe signals.
A few less common materials worth knowing
Polybutylene, used in residential supply systems for several decades primarily in late-century construction, has a documented history of premature failure and is now considered a repipe candidate wherever it remains in use. Lead supply pipes, present in some very old homes, are a health concern and a replacement priority on any inspection that finds them. Cast iron drain pipes, common in older homes, have a service life often exceeding many decades but eventually corrode internally and develop leaks at joints; cast iron drains in older sewer laterals are also where root intrusion most often appears, and replacement with PVC is the typical course when cast iron drains begin failing. Each of these materials has a context, and recognizing which materials are present in a given home is the first step in understanding what kind of plumbing the home actually has.
What’s actually in your home
Reading a home’s pipes is mostly a matter of inspection. Visible supply lines in basements, utility rooms, and under sinks reveal copper, galvanized, PEX, or CPVC at a glance. Visible drain lines reveal PVC or cast iron. The lines hidden in walls and under slabs are harder to verify without invasive inspection or building documents, but the visible portions of the system usually tell most of the story. A homeowner who can identify the material on the visible runs has the foundation for every other plumbing decision the home will require, from a single fixture repair to a full repipe.
