What Kind of Pipe Do I Have? Know Before You Buy Parts

Before you can fix a water line, you have to know what you’re looking at — because the right parts, the right tools, and the right amount of force are completely different for each kind of pipe. This matters most in mobile homes and older houses, where several generations of plumbing can be living under the same floor. Here is how a tech names them on sight, what each one does wrong, and what to replace it with.

CPVC — the yellowish one. Handle like glass, replace when you can

Spot it: rigid pipe in a slightly yellow, off-white color. Common in homes plumbed from the 1980s into the 2000s.

The problem: CPVC gets brittle with age. Old CPVC under pressure should be expected to crack — and not politely. Never cut old CPVC with ratcheting PVC cutters. The squeeze that cuts new pipe can split aged CPVC four or five feet down the line, turning a one-fitting job into a repipe.

If you must cut it (say, to swap a shutoff): a handsaw where there’s room. In the tight spots these pipes always live in, use a multi-tool on its low setting with a sharp blade, and hold the pipe steady with your hand at its base — pliers can crush it. Cut clean and don’t flex it. And don’t install new CPVC, or replace a bad section with more of the same: the real fix for CPVC is replacing it as you go.

Copper — soft runs and hard lines, and one big weakness

Spot it: the metal pipe, bright when new, green-tarnished with age. It comes in two forms. Soft copper is the small stuff — quarter-inch and three-eighths — run to furnace humidifiers and refrigerator ice makers, usually tapped into the side of a bigger line. Hard copper is the straight, soldered water line.

The problem: hard copper lasts a long time — that’s not its issue. It’s valuable (which makes it a theft target in empty houses), it costs a lot to replace, and it freezes badly: water turns to ice, expands, and rips holes right through the side of the pipe. The leak announces itself when things thaw. That’s why copper is a poor bet for mobile homes and any line that lives exposed to cold.

The gray pipe — polybutylene. The one plumbers groan about

Spot it: a plain gray flexible water line, usually three-eighths or half inch, sometimes three-quarter. You’ll know it when you see it — it just looks cheap.

The problem: this is polybutylene, the gray plastic pipe from the late 1970s through the mid-1990s, and it’s some of the worst pipe ever put in a house. It’s no longer sold. Its plastic connectors break as a hobby, the pipe itself is softer than modern plastic pipe (which is why its fittings need inserts inside the pipe to hold), and the original connections were a screw-on compression style that hasn’t aged any better than the pipe has. If your mobile home has gray pipe, plan on replacing it in sections as it fails — because it will.

Connecting to it takes a special fitting. Polybutylene’s wall and diameter aren’t quite PEX’s, so a regular PEX fitting can slip right off it. The fitting you want is a polybutylene-to-PEX transition coupling — SharkBite’s is the common one on the shelf, and it’s color-coded so you can’t mix it up: the gray collar goes on the polybutylene side, the tan collar on the PEX side, with a built-in tube liner stiffening the soft pipe. Ask for it by that name. A plain PEX coupling on gray pipe is a leak with a waiting period.

Modern PEX — red, blue, white. This is the good stuff

Spot it: flexible plastic tubing in red (hot), blue (cold), and white. This is what replaced everything above.

Why it’s the recommendation: PEX is easy to work with, cheap, and astonishingly freeze-tolerant — it can freeze solid sitting outside on concrete, thaw out, and not burst, because the pipe itself can flex with the ice. Its one weak point is the connections: anywhere the PEX meets a metal fitting is where freeze damage lands, because the metal can’t flex and cracks instead. Keep fittings somewhere warm or insulated and PEX is the most forgiving water line a homeowner can own.

Galvanized steel — hopefully you don’t have it

Spot it: dull gray metal pipe with threaded fittings, in genuinely old houses. It rusts from the inside out. If your water runs discolored and your pressure has been fading for years, galvanized is usually why. There’s no rescue for it — replacement is the only conversation.

The verdict, and how to buy for it

Repairing or replacing water lines? Go with PEX. Then make the second decision right: how you’ll connect it. Push-fit SharkBite-style fittings are genuinely good — for one or two connections. But they are expensive per fitting (a single push-fit shutoff can run $25–30, where a crimp-on PEX shutoff is a few dollars), and a real repair needs six to ten connections. At that count, buy a PEX crimp kit online — tool and rings together run under $100. The kit pays for itself in roughly eight connections or fewer, every future break is a five-minute job with parts you already own, and it’s simple enough to lend to a neighbor and talk them through it. That math is the whole ballgame for a homeowner doing their own plumbing.

STOP: any pipe work starts with the main water shutoff closed and the lines drained — and on old CPVC and gray pipe, assume the pipe is more fragile than it looks until you’ve proven otherwise. The most expensive plumbing mistakes happen in the first thirty seconds, with the wrong cutter on the wrong pipe.