Some more info:
The filter that blocked up is a Franke LB 2000 on a cold water line at a kitchen sink. Service to the meter is 3/4". Supply from the meter to the house is 1 1/4" copper. There is a new regulator (the old one had failed) set at 75 lbs. There are four baths, two kitchen sinks, and a laundry. Two to three folks in the house. I don't know about pipe markings, but I'll check next time I'm there.
The water company reported 0.1 ppm copper at the pressure regulator, 1.8 ppm in the cold water at a kitchen faucet, and 2.3 ppm in the hot water at the water heater.
We are a remodeling company working on this house. The owners have occupied it for only two years and were unaware of a water quality problem. Only a small amount of new plumbing work has been done in the course of the remodel: two new shower valves, relocating fixtures in the remodeled kitchen, the new regulator, and replacing the failed recirc pumps and adding check valves and expansion tanks at the water heaters. Work was done by a licensed plumber. The replacement pumps were sized based on the original pump model number. The plumber is looking into whether this is appropriate sizing but the pumps did not seem unusual for this purpose at the time he did the work.
Our work was almost complete when the owner reported reduced flow from the new Franke filtered water dispenser which led to the discovery of copper in the water.
Another question: Having determined that the problem resides in the house the water company will do no further testing. Whatever remediation is ultimately tried, we need to verify its effectiveness by testing for copper. Who does this kind of testing?