text: Cold water pitting of copper tube occurs in only a minority of installations.  Copper water tubes are usually guaranteed by the manufacturer against manufacturing defects for a period of 50 years. The vast majority of copper systems far exceed this time period but a small minority may fail after a comparatively short time.
  The majority of failures seen are the result of poor installation or operation of the water system. The most common failure seen in the last 20 years is pitting corrosion in cold water tubes, also known as Type 1 pitting. These failures are usually the result of poor commissioning practice although a significant number are initiated by flux left in the bore after assembly of soldered joints. Prior to about 1970 the most common cause of Type 1 pitting was carbon films left in the bore by the manufacturing process. 
  Research and manufacturing improvements in the 1960s virtually eliminated carbon as a cause of pitting with the introduction of a clause in the 1971 edition of BS 2871 requiring tube bores to be free of deleterious films. Despite this, carbon is still regularly blamed for tube failures without proper investigation.