What hardness actually is
Hardness is dissolved calcium and magnesium picked up from rock and soil, most common in groundwater moving through limestone. It is measured in grains per gallon (gpg) or mg/L. Using the USGS classification: below about 60 mg/L (roughly 3.5 gpg) is soft, and above about 180 mg/L (roughly 10.5 gpg) is very hard, with a common 'hard' threshold around 7 gpg.
It is not a health contaminant
Hard water is not federally regulated and is not treated as a health risk, which is why PurityMap excludes it from the health-based Purity Score. What it does cause is scale on fixtures and in appliances, spotting on glassware, and reduced soap lather.
A high hardness number is a maintenance-and-comfort signal, not a health one. It says nothing about PFAS, lead or disinfection by-products.
When a softener is worth it
If you have very hard water and notice scale shortening the life of water heaters and appliances, an ion-exchange softener or a salt-free conditioner can help. It is a lifestyle and maintenance decision, not a contaminant fix, and it does nothing for PFAS, lead or by-products. For the full comparison of softener, conditioner and RO, see do you need a water softener; to treat an actual health contaminant, see choosing a water filter by contaminant.
A note on sodium
Ion-exchange softening adds a small amount of sodium to the water. If a household member is on a sodium-restricted diet, consult a licensed healthcare professional, or consider a salt-free conditioner or a separate unsoftened drinking-water tap. Hardness itself is not a regulated health contaminant, so this is the main health-adjacent point to weigh.