I think you guys are correct that it’s the water especially if this happened at two places in the same area. A harsh mineral taste is most often caused by to much magnesium in the water. High levels of iron will also cause a mineral taste. However, reverse osmosis filters should easily knock down these minerals to acceptable levels even for pilsners with the addition back of the appropriate minerals for a given style. So it sound’s like the brewers may have been cutting corners.
Gotta pay attention to water quality, huh, Tom? Or am I tasting harsh tannins produced in a poorly executed mash?
The tannins from grain husks like those from grape skins produce an astringent bitterness but not mineral taste. As Tom pointed out tannins usually get into the beer during sparging. Mash temperatures, times and PH don’t release much tannins from the grain husks. However, sparging at to high a temperature and or for to long will. Also, water high in carbonates (calcium and magnesium) will also give the same astringent quality as tannins and enhance that of existing tannens.
Prior to large scale water treatments beer brewing was all about location, location, location. Now things are a little more flexible if you’re willing to work at it.