Overview
Two materials dominate residential potable water supply: copper and PEX. Copper is the long-proven metal standard, the pipe that ran clean water through American homes for generations. PEX is cross-linked polyethylene, the flexible plastic tubing that has taken over both new construction and repipe work in the last couple of decades. If you are plumbing a house or replacing failing lines, this is the choice you make first.
The decision comes down to a handful of things: cost, labor, how each behaves when it freezes, how long it lasts, and a few water-chemistry and code nuances that can flip the answer in specific situations. Copper wins on proven longevity and heat tolerance. PEX wins on price, install speed, and freeze behavior. Neither is wrong everywhere, and plenty of pros run both in the same house.
One thing to keep straight: this is the supply side, the pressurized lines that carry hot and cold water to your fixtures. Drain, waste, and vent (DWV) is a completely separate system, and it almost always uses PVC, ABS, or cast iron. Nobody runs copper or PEX for drains. Get the supply decision right first, then handle DWV on its own terms.
Copper Pipe
Copper is the metal that earned its reputation. It comes rigid (Type L for most supply work, Type M where code allows thinner wall) and soft (coiled, for tight runs and underground). It lasts decades, commonly 50 years or more, and a copper system installed correctly outlives the people who paid for it. It shrugs off heat, resists UV, and will not degrade sitting exposed in a crawlspace or running up an exterior wall.
Copper is naturally antimicrobial, which is part of why it stayed the standard for potable water for so long. It holds resale value, looks like real plumbing to an inspector or a buyer, and it is fully recyclable when you tear it out. There is a reason copper scrap has its own market.
The downsides are real. The material is expensive, and the labor is worse: soldered or pressed joints take a skilled hand, and because copper is rigid you need a fitting at every turn. It bursts when it freezes, no give at all. And in acidic or aggressive water it corrodes from the inside and develops pinhole leaks that can riddle a system years after install. Copper is the premium proven choice, and you pay for it both ways.
PEX Tubing
PEX is cross-linked polyethylene, sold in long coils and straight sticks in three flavors: PEX-A, PEX-B, and PEX-C. The differences come down to how the cross-linking is done and how the tubing handles expansion and kinks; PEX-A is the most flexible and most forgiving, PEX-B is the common value choice. All three carry potable water fine.
What sells PEX is speed and cost. The material is cheap, and you can snake a continuous run through framing like electrical wire, which means far fewer fittings and far fewer places to leak. You can plumb home-run style off a central manifold or trunk-and-branch like copper. It runs quiet, it tolerates freezing better than metal because it expands rather than instantly splitting (not freeze-proof, but more forgiving), and there is no torch: you join it with crimp rings, clamp rings, or expansion fittings.
The limits matter. PEX cannot go outdoors or anywhere UV hits it; sunlight breaks it down. It cannot connect directly to most water heaters; you transition with a short metal nipple off the heater. Rodents will chew it. The very-long-term track record is still maturing, and some insert fittings restrict flow more than you would like. PEX is the fast, cheap, modern default for good reason.
Head to Head
On cost, PEX wins clearly, both in material and in labor; copper is the premium on both lines. On install speed, PEX is far faster: it is flexible, runs through framing with minimal fittings, and skips the torch entirely, while copper means cutting, cleaning, fluxing, and soldering (or buying a pricey press tool) at every joint.
On freezing, PEX tolerates it better because it expands; copper bursts. PEX is not a license to skip insulation, but a hard freeze that splits copper will often spare PEX. On longevity, copper has the edge on paper: it has a proven 50-plus-year record, while PEX is rated for long life but simply has not been in walls as long. Time will settle that one.
On water chemistry, acidic or aggressive water pinholes copper from the inside; PEX is immune to that failure mode, though it is worth knowing your local water and the history of fitting recalls. On heat and UV, copper wins outright: PEX has temperature limits and dies in sunlight. On joints, copper's soldered or pressed connections demand skill, while PEX crimp and expansion joints are fast and forgiving. On code, both are widely accepted, but always check what your local jurisdiction allows before you buy.
Which to Use
For most new construction, repipes, and retrofits, run PEX. It is cheaper, it goes in fast, it tolerates freezing, and the continuous runs mean fewer joints to fail. If you are a homeowner doing your own work, PEX is the realistic DIY option; soldering copper well takes practice most people do not have. Freeze-prone runs through unconditioned space are another easy call for PEX.
Reach for copper where you specifically want the proven metal. That means exposed or exterior runs where UV and impact would kill plastic, the transition right at the water heater where temperatures spike, any high-heat application, and situations where your local water chemistry or a customer's preference favor it. Some inspectors and some buyers still see copper as the mark of quality work.
The honest answer for most jobs is a hybrid. A lot of pros run PEX for the bulk of the house, then stub out in copper or another metal at fixtures and transition to metal at the water heater. You get PEX cost and speed through the walls and metal where heat and exposure demand it. That combination is the working reality on a lot of modern jobs, and there is nothing wrong with it. If you are weighing the metal side on budget, the copper market moves; the copper prices page is worth a look before you commit to an all-copper bid.
FAQ
Is PEX safe for drinking water? Yes. PEX is approved for potable water across the country and carries the same hot and cold supply as copper. Early concerns about taste and leaching have largely been addressed in modern tubing; run the lines before first use to flush them, same as you would with any new plumbing.
Does PEX really survive freezing? Better than copper, not magically. PEX expands as water freezes instead of splitting instantly, so it often survives a freeze that would burst copper. It is not freeze-proof, though. A hard enough or repeated freeze can still fail it, so insulate runs in unconditioned space regardless of material.
Why does copper get pinhole leaks? Aggressive or acidic water attacks copper from the inside, eroding the wall until tiny holes form, sometimes years after a clean install. Velocity, water chemistry, and grounding issues all play in. If your area has a known pinhole-leak history, that alone is a strong argument for PEX.
Can I connect PEX directly to my water heater? No, not directly on most heaters. The heat right at the tank exceeds what PEX should see continuously. Transition off the heater with a short metal nipple or connector, then run PEX from there once you are clear of the hottest zone. Follow the heater and tubing manufacturer instructions.