Pinhole leaks in copper pipe

Entry in Choosing pipe and trouble · Updated October 29, 2026 · Written by the Know Your Pipes editors from the sources listed under References

Copper pipe pinhole leaks are small holes in copper water tube caused by pitting corrosion, a form of corrosion concentrated on a small area that penetrates the wall instead of thinning it evenly.^[1] Small ones are hard to detect, especially in pipes that run through walls and ceilings.^[1]

Pinhole leaks have been reported across the country but are more common in parts of some states, including Maryland, California, Florida and Ohio.^[1] The Copper Development Association describes corrosive water conditions as very infrequent and notes that widespread copper use in a locality is good evidence the local water is not aggressive to copper.^[2]

1 Causes

Researchers have offered several theories for pinhole leaks, and few causes are proven.^[1] The Copper Development Association groups copper corrosion problems under six causes.^[2]

Pitting waters typically have high total dissolved solids including sulfates and chlorides, a pH between 7.2 and 7.8, carbon dioxide above 10 ppm, and dissolved oxygen.^[2] Excess solder flux left inside the tube can cause or worsen pitting, especially if joints were overheated and the residue hardened.^[2] To limit erosion-corrosion and noise, the association recommends water velocities of no more than 5 to 8 ft per second, the lower figure for smaller tube, and warns that burrs left on cut tube ends create local turbulence.^[2]

Microbes are another proposed cause. A 2014 study of copper tube from Santa Fe, New Mexico, where 95% of local leaks were in cold-water lines, found microbes resembling actinobacteria deep inside the pits and concluded that microbial induced corrosion is a possible cause.^[3] The tube had leaked after about fifteen years of service.^[3]

2 Diagnosis and responses

Aggressive water can be identified by chemical analysis, and a qualified water treatment professional can specify treatment; this generally means raising the pH and removing or combining the carbon dioxide.^[2] For soft acidic water, raising the pH to about 7.2 or more usually solves the problem; on private wells, a common treatment is a bed of marble or limestone chips.^[2] Home test kits cover only part of this picture: Quality Water Treatment's water hardness test kit (Quality Water Treatment has the same owners as this reference), for example, measures hardness, while a pitting assessment also needs pH, chloride, sulfate and dissolved-gas figures from a laboratory.

A leaking section can be cut out and replaced; where leaks recur, the options include spot repairs, water treatment and repiping with PEX or new copper tube; which pipe for which job outlines the trade-offs. An active leak is handled first as a water emergency; see burst pipe: first steps.