Good question. I don't know. I have a water softener in our house (installed in 2003)... It takes our well-water that's 240-330PPM seasonally and outputs it at ~300PPM. In talking to water people, most likely that's exchanging mineral hardness for sodium. I've seen the potassium before, but haven't tried it out in our system.
It looks like they posted a report from their water municipality that is delivered as tap water prior to any additional treatment a homeowner might provide. You definitely don't need a water softener with that water. Looks like they're good to go with straight tap water.