The stain looks like an oil slick in a parking lot. The water didn’t smell or taste funny. There was a huge water filtration system (like 6 ft. tall) but I don’t think it was on.

Does anybody know what would cause this?

And will the filtration system fix the water?
Thank you for the comet message. Thanks for the chuckle.

But I am more curious about the water rather than the sink.
Once again, thanks for the cleaning suggestion… I should be good in that department.