u/AWhaleOfAWife

Just now I was pouring some warm tap water from my kitchen sink into a measuring cup and after it filled I saw all of this black substance float to the surface. The cup is not dirty - this is the second time I filled it and the first time, moments before, this did not occur. It appears to be an oily substance that breaks down when I rub it between my fingers. Does anyone know what this might be? My home is roughly 25 years old and I’ve never seen this in the past year I’ve been here. I use this sink frequently - it has not been sitting unused.

Placed on my laptop for visual clarity as my countertop is patterned.