Actually, all this was sounding like an X-files episode to me. As for more info:No oil wells or oil storage areas or pipelines nearby. And no standing water in the vicinity either. Water comes from city mains(no wells)in metal pipes.She lives in the south suburban Chicago area. This black stuff is coming out of every fixture in the house (three) and in every toilet. "Backwash"- I believe meaning the flow in the toilet tanks when filling, happends in all three toilet tanks and several times a day. I didn't notice a smell(have to get my nose closer to it). I told my mom to call her village hall with this problem. Apart from that I recommended bottled or filtered water for drinking and cooking.