I learned this when I tried making coffee using water from an RO unit. It was just kind of flat. I switched to filtered tap water and got better results. We get

I learned this when I tried making coffee using water from an RO unit. It was just kind of flat. I switched to filtered tap water and got better results. We get water from Lake Michigan which AFAIK has hardness about 135 ppm. I wish they had included Chicago it in the graph.