There are two conditions that can cause a pinhole leak in copper pipe: mixed metals in the plumbing and acidic water. These conditions cause internal corrosion of copper pipes.
When galvanized and copper plumbing are connected in the plumbing of a house or building, electrolysis can happen. To prevent this reaction connect them with a dielectric fitting. This reaction also occurs when a ground wire touches a galvanized connection on a hot water heater. When electrolysis is ongoing, the copper pipe is pitted by corrosion, leading to a pinhole leak in the copper pipe.
Acidic water corrodes the copper, eventually causing a pinhole leak in the copper pipe. There are three kinds of pitting corrosion not related to mixed metals.
- Type one pitting is related to hard water that has a pH level of 7 to 7.8. This is usually associated with cold water. The pitting is deep and spare. It causes pipe failure.
- Type two pitting is related to soft water that has a pH below 7.2. It normally doesn't happen when the temperature is below 140 degrees F. This pitting is also narrow and causes pipe failure.
- Type three pitting is related to cold water that has a pH level over 8.0. This pitting is wide and shallow and causes pipe blockage or blue water.