[Noah930]

Nothing sticking to a magnet.

House was built in 1947. It's a rental, so I don't know the history of the place re:renovations and piping. House gets water from the city; no wells.

I don't recall seeing any water main work in the neighborhood, recently. I'll ask the neighbors if they're having any similar problems.

Interesting that it's only happening to the three tubs and the one shower. Not the bathroom sinks, kitchen sink, or outside spigots. Haven't run the dishwasher or clothes washer, yet. Filter screens on the couple I've pulled off (from the sinks that are clean) haven't had anything trapped behind them.

I ran the tub for 10 minutes this morning, and quit after a little riverbank of stuff started accumulating.

Thanks for the replies.