What hardness actually is
Hardness is dissolved calcium and magnesium that water picks up moving through limestone and other mineral rock — so it is most common in groundwater. It is measured in grains per gallon (gpg) or milligrams per litre (mg/L). Using the USGS classification, water below about 60 mg/L (roughly 3.5 gpg) is soft, and above about 180 mg/L (roughly 10.5 gpg) is very hard; a common 'hard' threshold sits around 7 gpg.
It is a comfort issue, not a health one
Hard water is not federally regulated and is not treated as a health contaminant, which is why PurityMap excludes it from the health-based Purity Score. What it does cause is scale on fixtures and inside appliances, spotting on glassware, reduced soap lather, and shorter life for water heaters and other water-using appliances.
A high hardness number is a maintenance-and-comfort signal, not a safety one. It says nothing about PFAS, lead or disinfection by-products, which need their own treatment.
How to find your hardness
Hardness usually is not in the federal datasets — it appears in a utility's own annual Water Quality Report (Consumer Confidence Report). Where PurityMap has not yet sourced that document for a system, it marks hardness as pending rather than guess a number. You can also measure it yourself with an inexpensive home hardness test, which is enough for a softener decision.
Softener, conditioner, or RO?
An ion-exchange water softener removes calcium and magnesium and replaces them with a small amount of sodium — the classic fix for scale, but worth noting if anyone in the home is on a sodium-restricted diet. A salt-free conditioner reduces scale buildup without removing the minerals and adds no sodium. Reverse osmosis is a point-of-use option for drinking water, not a whole-house softener. Match the choice to your goal.
When a softener is worth it
If your water is very hard and you are seeing scale shorten appliance life or coat fixtures, a softener or conditioner can be a reasonable maintenance investment. It is a lifestyle-and-plumbing decision, not a contaminant fix — so if your real concern is PFAS, lead or by-products, a softener is the wrong tool. To match treatment to a health contaminant instead, see choosing a water filter by contaminant. PurityMap may earn an affiliate commission on some product links, at no cost to you.
A note on health
This article covers hard water, which is not a regulated health contaminant. The one health-adjacent point is sodium: ion-exchange softening adds 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.