cold water supply - copper line turning black


While doing an inspection the other day I ran across the cold water lines in the basement turning black. I’ve researched the issue on this forum and found several considerations but nothing solid to hang my hat on.

One other thing noted by the home owner was that at the kitchen sink, when they first turn on the cold side of the faucet (two handle faucet) it will run very warm to hot for a short while before running cold. I checked the basement and didn’t see anything that would be causing the cold supply line to be heating up at rest. This was more prevalent when the faucet wasn’t used for a considerable time.

Don’t know if these two issues are related or separate.

Any thoughts? There was some recent drywall work done in the basement within the past year, but I would have thought that Chinese drywall would be out of circulation and therefore, not something to consider.

Thanks for the feedback in advance.

Steve W.

Cold water pipe goes straight down to water heater allowing cold to circulate in the cold pipe see Proper installation guide . Stains can have many causes example Cat pee Storage of chlorine or other chemicals . Try a Google search .

Another question that comes to mind, if a Shark-Bite is used in line of a copper run should there be additional bonding from one side of the connector to the other? This question would also pertain to using PEX.

Steve W.

Thank Roy, but the problem goes well past the W/H. And no cats in the home.

Sharkbite plumbing fittings do not preserve the electrical continuity .

I stand with my report on hot water circulating a long way in pipe .
Unless there is a recirculating pump in the system …
I have one but use a separate return not the cold water return .

Eight years love it never be with out one again

Where I am copper water lines turn black when summer humidity is too high in the basement and condensation forms on the cold water lines. When I see this the hot water lines are typically brown like an old penny, cold lines look like they were painted with matte black paint.
re the hot cold water, something is warming the line, most likely a hot water line not too far away. No biggie

That looks like a pretty cool set up. And seems to be pretty easy to install.

Thanks Erik.