Quick Answer
USGS public data shows hardness varies strongly by region: the Midwest and Southwest generally have harder groundwater, while the Northeast and Pacific Northwest tend to be softer. These are broad patterns — the authoritative number for your home is in your utility's water quality report.
Problem
Hardness affects soap scum, scale, and appliance life, but most people have no idea whether their region is hard or soft.
Product Recommendation
A shower filter does not soften water. For hardness, research softeners; for the shower experience, ZOOSHEN targets chlorine/chloramine. See /water-science/water-hardness-units.