Pinhole leaks in copper pipes: causes, Greenville water and when to repipe

By the GVL Plumbers editorial team · Published Oct 31, 2026 · 8 min read · Filed under Pipes & older homes

Pinhole leaks in copper pipes are maddening because they don't seem fair. Copper is supposed to last a lifetime, the pipe looks fine from outside, and then a stain appears on the ceiling under the bathroom. You cut out the drywall and find a hole you could barely fit a pin through, spraying a fine mist that's been running for weeks.

The good news is that a single pinhole is a simple fix. The harder question is whether it's a one-off or the first of many, and that depends on why it happened.

What causes pinhole leaks in copper pipes

Copper normally builds a thin, stable film on its inner surface that protects it. A pinhole forms where that film breaks down in one small spot and corrosion digs straight through the wall instead of spreading out. That's called pitting. A few things are known to drive it.

Water chemistry

The best-known research comes from Virginia Tech, where Marc Edwards and his students spent years recreating pinhole outbreaks in the lab, funded in part by the National Science Foundation. They tested hundreds of water recipes. Factors linked to more pitting included higher chlorine levels, aluminum in the water, and less natural organic matter. One counterintuitive finding: raising the pH to about 8.5 to 9 together with high chlorine was especially damaging. In some pits they also found sulfate-reducing bacteria, which points to a biological cause in some cases.

That work also found pinholes could be produced without stray electrical current, lightning or poor plumbing practice. Those things can still contribute, but they aren't required.

Velocity and erosion

Fast-moving water, particularly hot water, can scour the protective film away, usually right after an elbow, tee or burr where the flow turns turbulent. The Copper Development Association's design guidance puts the upper limits around 5 to 8 feet per second for cold water, 4 to 5 feet per second for hot water under 140°F, and 2 to 3 feet per second above 140°F. Undersized pipe and hot water recirculation pumps running too fast are the classic culprits.

Installation

• Pipe ends that weren't reamed after cutting leave a lip that creates turbulence.
• Excess soldering flux left inside the pipe can keep corroding the wall near joints.
• Pipe that was kinked, dented or bent too tightly.
• Copper touching steel or galvanized pipe without a dielectric fitting.
• Pipe that rubs on a joist or strap and vibrates.

Stray current and grounding

People blame electrical grounding a lot, and it can matter, but the Virginia Tech work suggests it's not the usual driver. If you see leaks clustered near where the electrical ground clamps to the water pipe, it's worth having an electrician check the grounding. Otherwise, look at chemistry, speed and installation first.

Is Greenville Water's water aggressive to copper?

Left untreated, Upstate surface water would be. Greenville Water's reports show it as very soft and low in alkalinity, the kind of water that tends to be corrosive to metal pipe. The utility has run a corrosion control program since the mid-1970s, and SC DHEC (now SC DES) approved it under the federal Lead and Copper Rule. What the utility does, in its own published numbers:

Our read: the treatment is doing its job for general corrosion. Copper at the tap is low across the system. That doesn't rule out pinholes, which are a local, spot-by-spot problem that a tap copper test doesn't measure. We didn't find any Greenville Water statement about pinhole leaks, or any public report of a pinhole outbreak in its service area. If your house gets them, the cause is more likely in the house (velocity, installation, an old recirculation setup) than in the water. If you're on Greer CPW or another provider, its annual water quality report lists the same kind of figures.

Private wells are a different story. Well water isn't treated by anyone but you, and a well with low pH can eat copper from the inside. If you're on a well and getting pinholes, a water test is the first step, before any pipe work.

Signs of a pinhole leak

• A water stain, bubbling paint or soft drywall, often on a ceiling below a bathroom or along a wall near the water heater.
• A musty smell in one room or closet that doesn't go away.
• Green or blue crust on the outside of exposed copper, or a small white or green spot with a damp halo.
• A faint hissing in the wall when the house is quiet.
• A water meter that moves with every faucet off.
• In a slab house, a warm spot on the floor if it's a hot line.

The meter test is the fastest check. Turn off every faucet and appliance and watch the meter's leak indicator for 15 minutes. Our leak detection guide explains how plumbers find leaks behind walls without tearing out everything.

Temporary fixes until a plumber arrives

First, shut the water off. If the leak is on a branch you can isolate, close that fixture's valve; otherwise use the main. If it's a hot line, turn off the water heater too. Then, if the pipe is reachable:

1. Pipe repair clamp. A rubber-lined clamp sized to the pipe, centered over the hole. It's the most reliable stopgap.
2. Epoxy putty rated for plumbing. Dry and sand the pipe first, or it won't stick.
3. Self-fusing silicone repair tape, stretched tight and wrapped well past the hole.
4. Push-to-connect coupling. Cut out the bad inch of pipe and join the ends. This can be a lasting repair if it's done right and left accessible.

Clamps, putty and tape are meant to buy days or weeks, not years. If the leak sprayed into a wall, dry it out quickly; our burst pipe guide covers water damage cleanup.

When to repair and when to repipe

Here's the decision guide we'd use for a Greenville County house:

When people repipe because of pinholes, PEX is the usual choice. It doesn't pit and handles soft water fine. Some homeowners stick with copper because they like it. That's reasonable if the cause was installation, but if the house has had pinholes all over, we'd go with PEX. Our repiping guide covers the process, and the cost guide covers what drives the price.

A few other things to weigh:

• Insurance. Each water damage claim goes on your record, and several in a row can affect renewal. Ask your agent how they treat repeat leak claims.
• Age. Older houses may have a mix of copper and galvanized. Our older homes guide explains what each era typically has.
• Selling. Repeated leaks are worth disclosing and worth fixing before a buyer's inspector finds the stains. See our home buyer's plumbing checklist for what inspectors look for.

Pinholes aren't the only reason copper or plastic supply pipe fails. If your 1980s house has a gray plastic line mixed in with copper, read our guide to polybutylene pipe too.

Pinhole leak questions