Pinhole Leaks in Copper Pipes: Causes, Signs and Repair Options

A pinhole leak is exactly what it sounds like: a hole in a copper pipe so small you can barely see it. It can spray a fine mist inside a wall, drip onto a ceiling, or soak the soil under a slab for months. And where there’s one, there are often more. Here’s what causes them, how to find them, and when to stop repairing and start replacing.

What causes pinhole leaks

Pinholes start as pitting corrosion on the inside of the pipe. Common drivers:

• Water chemistry: pH, hardness, dissolved minerals and disinfectants like chlorine or chloramine all affect how copper corrodes. Central Indiana’s hard water is one factor, but chemistry varies by utility and over time.
• High water velocity: water moving too fast, especially in recirculating hot water lines or undersized pipe, scours the pipe wall. This is called erosion corrosion.
• Turbulence: at elbows, tees and poorly reamed cut ends.
• Thin-wall pipe: Type M copper has thinner walls than Types L and K, so it has less metal to lose.
• High water pressure: increases velocity and stress.
• Stray current or poor grounding: can accelerate corrosion in some cases.

Signs of a pinhole leak

• A tiny spray or drip on an exposed pipe, often with green or blue staining
• Stains or bubbling paint on a wall or ceiling
• A water meter that moves with everything off
• A hissing sound in a wall or under the floor. See hear water running when nothing is on.
• Warm spots on the floor from a hot-side pinhole under a slab
• A higher water bill

Finding a hidden pinhole

A pinhole in an exposed basement pipe is easy to spot. One inside a wall or under a slab is not, and it makes very little water at first, so the damage builds slowly.

With slab leak detection and hidden leak detection, we:

1. Confirm the leak with a meter test and isolate the hot, cold and service lines.
2. Pressure-test the suspect line.
3. Listen with acoustic equipment for the hiss of the pinhole.
4. Scan with a thermal camera for the warm or wet pattern.
5. Mark the spot for the plumber.

See how to find a slab leak for the signs and home tests.

Repair options

Option	When it fits
Repair clamp	Temporary fix on an exposed pipe until a plumber arrives
Cut out and replace the section	One pinhole in a line that’s otherwise in good shape
Reroute the line	Pinhole in a slab line; bypasses the old line through walls or the attic
Repipe	Several pinholes in a few years, thin or badly pitted pipe throughout

Epoxy putty and tape are emergency stopgaps, not repairs.

When to stop repairing

Pinholes come from conditions that affect the whole system, not one spot. A good rule of thumb:

• One pinhole: repair it, and keep an eye on the meter.
• Two or more in a few years, or a plumber finds thin, pitted pipe when making the repair: get a quote to reroute or repipe. See whole house repipe cost.
• Pinholes under the slab more than once: rerouting overhead usually beats repeated slab repairs. See slab leak repair cost.

Reduce the risk

• Check your water pressure. Keep it under 80 psi with a working pressure-reducing valve.
• Ask your utility about water chemistry changes if pinholes start appearing across your neighborhood.
• Have a plumber check that hot water recirculation pumps aren’t running too fast.
• Get pinholes found early, before water damage spreads.

Get it found

We find pinhole leaks in walls and under slabs across Bargersville and Johnson County, including Greenwood, Center Grove and Franklin, and mark them for repair.