J Kupper:–The green stains are an indication that there is a corrosion process at work within your piping system. Green stains are from Copper Chloride…Blue stains are the result of Copper Sulfate. The site below may answer some of question in this matter, and explain what options are available to prevent leaching of copper into your drinking water or the formation of pin hole leaks………Bud.hello, : I heard that green copper stains in the sink could be an indication of problems with the copper piping. How can I check whether the piping is ok? : thanks, : J. Kupper