I’m seeing more and more of this types of corrosion on the cooper water pipes. I generally see corrosion at the soldered joints and at hangers/supports and more so with older homes in the 70’s/80’s. Very rarely do I see actual leaks from these locations and know its only a matter of time.
I’m curious how you guys are writing this up without causing alarm but at the same time letting buyer know this is something he needs to pay attention to. Looking for improvements to my narrative.
“Basement, I saw heavy corrosion and a build-up of mineral deposits on the copper water pipe in several locations today. This is an indication the piping is failing and may leak at anytime. There was no active leaks at time of inspection. I recommend further evaluation and correction by qualified and licensed plumber to help prevent water damage to personal items and structure if leak should occur.”
Here is a pretty good reference for Cause Of Corrosion in Copper pipe.