Why does my water supply line have a sudden pinhole leak?

What a sudden pinhole leak actually means

A pinhole leak is a tiny hole in the pipe wall, usually smaller than the tip of a pen. It weeps or sprays a fine stream depending on your water pressure.

On copper, it almost always means the pipe corroded through from the inside. The water chemistry, or how fast water moves through the pipe, ate the wall until it broke through.

It feels sudden because the corrosion is invisible until the last moment. The green or blue crust you see on the outside is the leak announcing itself, not the start of the problem.

The good news: a single, accessible pinhole is a genuine DIY repair for most people. The bad news: it's often a warning that the rest of that pipe run is aging the same way.

Why your supply line pinholed

Most pinholes trace back to one of two things: your water is corrosive, or it moves too fast through the pipe.

Corrosive water means low pH, high chlorine or chloramine, or high dissolved minerals. Over years, it pits copper from the inside. This is why some neighborhoods see pinholes constantly and others never do. It's the water, not bad luck.

High velocity is the other big one. If your pipes are undersized for your fixtures, or your pressure runs above 80 psi, water scours the inside of elbows and tight bends. The leak shows up right where the turbulence is worst, usually just downstream of a fitting.

The rest of the causes are more localized: a solder joint that was never quite right, a PEX crimp that didn't seat, a spot that froze last winter, or two dissimilar metals corroding where they meet.

Figuring out which one you have tells you whether to patch and move on, or start planning a bigger fix.

• Green/blue crust on copper: internal pitting corrosion
• Leak right after an elbow: high velocity erosion
• Water beading at a fitting seam: failed joint, not the pipe
• Leak on PEX: almost always a connection, not the tubing
• Copper-to-steel junction: galvanic corrosion

What to do in the next hour

First move is always the same: stop the water. If there's a shutoff for that fixture or branch, use it. Otherwise go to the main where the line enters the house.

Open a faucet lower than the leak to drain the pressure and let the pipe empty. This makes the repair dry and safe.

Dry the pipe with a rag and watch where the water comes back. You need to know the exact spot, and whether it's the pipe wall or a fitting edge. This is the single most important thing you'll do, because it decides the whole repair.

Measure the pipe. Half-inch copper has an outside diameter of about 5/8 inch; 3/4-inch copper is about 7/8 inch. Get this right or your fittings won't seat.

If you need water back tonight and can't do the real fix yet, a stainless repair clamp or a push-fit coupling will hold. Just know it's temporary and check it daily.

For the permanent fix, cut out the bad inch or two and slide in a new coupling. Push-to-connect fittings make this no-torch and beginner-friendly.

What it costs in 2026

That covers a couple of push-fit couplings ($12 to $18 each), a pipe cutter if you don't own one ($15 to $30), and a repair clamp for backup.

A licensed plumber runs $150–$500 for a single accessible repair. That's the trip charge, the minimum labor block (usually one to two hours), and materials. Most of that number is showing up and doing it right, not the parts.

The price jumps once the pipe is behind drywall or above a finished ceiling. Now you're paying for access, the repair, and often a drywall patch afterward. That can push a simple fix past $1,000 with the finish work.

If you've got multiple pinholes on the same copper, get a re-pipe quote. Whole-house PEX re-pipes typically land between $4,500 and $12,000 depending on home size and access, but they end the game instead of you paying $500 every few months.

• Professional repair typically runs $150–$500. This is not a DIY job, so plan on hiring a pro.
• Pro single accessible repair: $150–$500
• Behind-wall repair with drywall patch: $700 to $1,200+
• Whole-house PEX re-pipe: $4,500 to $12,000

Should you DIY this or call someone

DIY makes sense when the leak is on exposed pipe (basement, crawlspace, under a sink) and it's a single spot. Push-fit couplings mean you don't even need a torch.

The skills you need are basic: shut the water, cut the pipe square, deburr the ends, and push the fitting on to the marked depth. Anyone comfortable with a pipe cutter can handle it.

Call a pro when the leak is inside a finished wall or ceiling, when you're finding leaks in clusters, or when the fix involves soldering near framing and you're not confident with a torch.

Also call a pro for anything upstream on the main, like a pressure-reducing valve. Working on the main service line is regulated in most jurisdictions and not worth the risk.

Can this wait, or is it urgent?

A pinhole is high urgency. Even a slow weep doesn't stay slow. Corrosion holes widen, and the day one blows open you can lose gallons a minute.

If you can shut off just the affected branch and leave the rest of the house working, you've got a little breathing room to do the repair right this week.

If the only shutoff is the main, you're choosing between no water and a controlled leak into a bucket. That's a same-day fix.

The hidden risk is water you can't see. A pinhole spraying into a wall cavity or over insulation rots wood and grows mold in a couple of days. Don't wait on those.

Does your home's age matter? Yes.

Homes plumbed with copper from the 1970s through the late 1990s are the most common pinhole victims. Decades of aggressive water chemistry finally catch up.

If that's your house and you're on original copper, one pinhole is a strong hint the rest of the system is close behind. Start budgeting mentally for a re-pipe even if you patch this one.

Homes from the 2000s on are more likely PEX, which almost never pinholes. A leak on PEX points you straight to a connection or a nicked line, not the tubing itself.

Older homes with galvanized steel don't pinhole the same way; they corrode and clog and leak at threaded joints. If you've got a mix of copper and galvanized, watch the transition points closely.

How we put this together

This guide reflects patterns field techs see on real service calls: which causes actually show up, in what order to rule them out, and where DIY stops making sense.

Cost ranges are 2026 US figures blending national labor rates, current fitting prices, and typical trip-charge structures. Your local rates vary, especially in high-cost metros.

The DIY-versus-pro lines are drawn on safety and code, not just difficulty. Open-flame work near framing and anything touching the main service line belong with a licensed plumber.

When in doubt, shut the water off and take the extra day to do it right. A dry house is cheaper than a fast fix that fails.