From a pinhole to a burst

Copper pipe usually lasts a long time, but it can corrode from the inside in small, concentrated spots. The result is a pinhole: a tiny opening that may only mist or drip at first. Inside a wall or under a slab, that drip can run for weeks, soaking framing or concrete before anyone notices.

Under constant pressure, the metal around a pinhole keeps wearing. A leak that started as a drip can open up and spray, which is when most homeowners first realize there is a problem.

Copper pipe terms you may hear

Type M, L and K
Copper pipe wall thicknesses. Type M is the thinnest and was common in homes; L and K are heavier.
Pitting corrosion
Corrosion concentrated in small spots rather than spread evenly, which is what produces pinholes.
Erosion corrosion
Wear from fast-moving or turbulent water, often just past elbows and fittings, and more common on hot lines.
Sweat joint
A soldered copper joint. A drip at a joint is a different problem from a pinhole in the pipe wall.
Repair coupling
A short fitting used to splice in new pipe after the damaged section is cut out.

Signs of a pinhole you have not found yet

  • Blue-green stains on copper pipe or the surface under it
  • A faint hiss behind a wall when nothing is running
  • Bubbling paint or soft drywall in one small area
  • The water meter's leak indicator moving with every tap off
  • A warm spot on the floor, which suggests a hot line under the slab
  • Previous pinhole repairs on the same line

What causes pinholes

Pinholes have several possible causes and often more than one at a time: water chemistry, high flow speed in undersized or hot lines, debris left from installation, stray electrical current on grounded pipe, and thin-wall pipe. Hard water is part of the local picture, but a plumber looking at the removed pipe is the best way to judge what happened in your house.

Choosing the repair

  • IfThis is the first pinhole and the pipe looks sound around itThenA spot repair, cutting out a short section and splicing in new pipe, is usually reasonable.
  • IfThere have been several pinholes in the same runThenAsk about replacing that run, since the pipe is likely thin in other places too.
  • IfPinholes keep appearing on hot lines under the slabThenAsk about rerouting the hot lines overhead rather than repeatedly opening the floor.
  • IfPinholes show up all over the houseThenGet a repipe evaluation and compare it with the cost and disruption of continued repairs.

Common questions

Why do pinholes keep showing up in the same house?

The conditions that caused one pinhole, such as water chemistry, flow speed or thin pipe, usually affect the whole system. Repeat leaks are common once they start.

Are hot or cold lines more likely to get pinholes?

Hot lines are often more affected because heat and higher flow speed in recirculating or undersized lines speed up wear, but cold lines can fail too.

Should I ask for the removed pipe?

Yes. Seeing the inside of the pipe helps you and any later plumber understand whether the problem is local or widespread.

General information for Fullerton, not a quote or professional advice. In an emergency, call 911.