Quick answer
A pinhole leak is a tiny hole that corrosion or erosion wears through a copper pipe wall, often hidden inside a wall or ceiling. Sources point to water chemistry, fast water velocity from high pressure, and installation problems, and they do not agree on one cause. A single leak can be spot repaired, but repeated leaks usually call for evaluating a repipe.
What a pinhole leak is
A pinhole leak is a tiny hole in a copper water pipe, often too small to see at first. Butler County, Ohio's water and sewer department describes them as small pits of corrosion on the inside of a copper pipe that eventually break through the pipe wall.
Because the hole is so small, water may seep or spray in a fine stream for a long time inside a wall, ceiling or crawlspace before anything shows on the surface. The county also says scientists have not determined exactly why the pitting happens and that there is usually no consistent pattern. That honesty is worth keeping in mind as you read the rest of this guide: the causes below are what sources report, not a diagnosis of your house.
Signs to look for
Plumbing company Mr. Rooter lists the following warning signs. No single sign proves a pinhole leak, and several overlap with other problems, so more than one together is a stronger signal.
- Damp spots, water stains or discoloration on walls, ceilings or floors.
- Green or blue-green stains on exposed copper.
- The sound of running or dripping water when every faucet is off.
- An unexplained rise in your water bill.
- Musty odors or mold near pipes, basements or crawlspaces.
What sources say about water chemistry
The best known research comes from Marc Edwards, a Virginia Tech engineer. In a 2008 Science News report, he concluded that in the cases he studied the water had become more corrosive, not the copper weaker. In his lab, raising pH to roughly 8.5 to 9 and adding chlorine caused severe pitting. He also pointed to the removal of organic matter from treated water, which can strip away natural protective residues, and to cement-lined water mains that leach lime and raise pH. He reported preliminary, then unpublished, findings about sulfate-reducing bacteria in pits.
Utilities have reached similar suspicions. A 2004 fact sheet from Maryland's WSSC Water said investigators found no obvious problem in its routine water chemistry records, noted that Edwards's lab work did not by itself prove pinholes form in pipes, and described adding orthophosphate to the water in November 2003. In 2020 the City of Folsom, California released a consultant study suggesting very pure water with a pH above 9.0 and chlorine could cause pitting, and began adding orthophosphate. The city said it had not determined why the pH rose.
Velocity, pressure and installation
Not every source blames the water. Stonegate Village Metro District says erosion from high water velocity wore away the inside of the pipes in its area, that nearly all its reported leaks came from this, and that high velocity is most often caused by high pressure. The district recommends a pressure reducing valve in every house and says normal pressure is 45 to 65. Mr. Rooter says pressure above 80 psi increases velocity and wears the pipe lining, especially at bends and fittings.
Installation and manufacturing also come up. Butler County lists substandard pipe manufacturing, improper installation, improper electrical grounding and excess plumbing flux. Mr. Rooter adds tight bends, dents, scratches and drips of solder or flux inside the pipe. It also says copper typically lasts 20 to 50 years and that most pinhole leaks appear around 25 to 30 years, which is one plumbing company's figure rather than a measured standard.
Where the sources disagree
Read together, the sources describe different places with different water. Edwards, WSSC and Folsom emphasize chemistry. Stonegate emphasizes velocity and calls corrosion less common inside houses. Butler County says no pattern has been found. Those findings may all be true in their own settings, which is why one cause cannot be assumed for your home.
They also differ on prevention. Butler County says there is no way for a homeowner to prevent a pinhole leak. Stonegate and Mr. Rooter point to pressure control, and Mr. Rooter mentions water softeners as preventive measures. Treat these as ideas to discuss with a plumber and your water utility, not guarantees.
Spot repair or repipe
Mr. Rooter says tape and clamps are only temporary and that corrosion is often present elsewhere in the system. Butler County notes you can patch a pinhole with a hardware store clamp or call a plumber. A spot repair may be enough for one isolated leak, but a plumber should look over the rest of the system first.
The same company suggests a repipe may be more cost effective than patching one leak at a time when copper is very old or thin walled and leaks keep returning. It recommends professional help if you have more than one leak, a home 25 or more years old with original copper, or a steadily rising water bill. These are general rules of thumb from one company, so the decision should rest on an inspection of your actual pipes. This article does not quote prices because the sources reviewed did not give reliable ones.
Questions to ask a plumber
Before agreeing to a spot repair or a repipe, it helps to ask:
- Where exactly is the leak, and what does the pipe around it look like?
- Is the rest of the copper in similar condition, and how can you tell?
- What is my water pressure, and is a pressure reducing valve present and working?
- Is this repair meant to be temporary or lasting?
- If I repipe, what material will be used and what opening and patching of walls should I expect?
- Can the scope of work and any warranty be put in writing?
- What should I tell my insurance agent? Butler County advises checking coverage before a problem happens, since water damage and replacement costs may not be fully covered.
When to call Pyper Plumbing
If you see water coming through a ceiling or wall, hear water running with everything off, or find a wet spot that keeps coming back, shut off the main water valve and call. Pyper Plumbing offers emergency plumbing repair, leak detection and repair, and repiping for homes in Snohomish, Skagit, Whatcom and Island counties.
If you are only seeing early signs, such as green stains or a creeping water bill, an inspection can help you decide between a spot repair and a larger plan before a small leak turns into a damaged wall.
Common questions
Can I fix a pinhole leak myself?
A clamp or patch can slow a leak temporarily, and Butler County, Ohio notes it as an option. Mr. Rooter cautions that corrosion is often present elsewhere, so a plumber should look at the whole system rather than rely on one patch.
How long do copper pipes last before pinhole leaks start?
Sources differ. Mr. Rooter says copper typically lasts 20 to 50 years with most pinhole leaks around 25 to 30 years. This Old House, citing the International Association of Certified Home Inspectors, lists copper water lines at 70 years. Water chemistry and pressure probably explain part of the gap.
Does a pinhole leak mean I need to repipe?
Not necessarily. One isolated leak may be repaired. Repeated leaks, thin or very old copper, or several failures in a short time are the situations in which sources suggest weighing a repipe.
Sources
Facts in this guide come from the following references. Local rules and manufacturer instructions can differ, so follow your utility and your equipment manual.
- Holey copper pipes, Science News (Janet Raloff, 2008)
- WSSC Water, Pinhole leak investigation fact sheet (March 2004)
- CBS Sacramento, Folsom finds possible source of pinhole leaks in copper pipes (October 21, 2020)
- Stonegate Village Metro District, Pin hole leaks
- Butler County Water & Sewer (Ohio), Pinhole leaks
- Mr. Rooter Plumbing, What causes pinhole leaks in copper pipes and how to prevent them
- This Old House, How long do appliances and parts of your home last
This guide is general information, not a substitute for an on-site inspection. If you smell natural gas, leave the building and call 911 or your gas utility. Pyper does not perform gas line work.
