[cwl1979]

Carl,

According to the certification numbers, that’s an antibacterial silver nitrate water filter.  Some version was installed in lots of coaches back then.

Great idea in theory.  No company lasted long enough to get to sell replacement inserts.    Those are typically needed after ~70,000 gal through the filter.

That's interesting. Some google research comes up with really nice facts about using silver nitrate in conjunction with charcoal for fresh water cleaning. Shows it can kill almost all bacteria and most fungus as well. It wont harm algae though. 
Thanks for that wisdom.