I'm very thankful for your help.
The taste and odor bother the whole family.
The galvanized pipes are 30 years old. I'm not seeing rust stains yet, but I know it's coming.
From prior experience, I know galvanized pipes sluff lime or calcium. In my opinion, the water is hard. Galvanized pipes in this area tend to loose flow as time goes on.
I don't plan to do the whole house, just the drinking water at the sink.
Also, I've tried other twin cartridge units before, and never knew when to change them - the flow rates never changed much, it was always slow.