Thanks. Should have googled.

However, upon closer inspection, it seems like there was a wave of research during 1960s which looked at Copper ion concentration between 0.02 - 10g/L

In the 2000s there was another wave of research looking at antimicrobial properties, however sampling a few of them, it does seem like they were seen as growing surfaces rather than containers for water purification.

So, I guess it was observed for a long time, scientifically studied fairly recently, and not in particular whether it was viable in a practical setting?