Before you size a softener, you need one number: your water’s hardness. Here’s where to find it and how to read it.
What hardness is (and isn’t)
The USGS (checked 2026-10-19) defines hardness as the amount of dissolved calcium and magnesium in water. It causes soap scum, spotty glasses, and scale in water heaters and pipes. The USGS also says hardness “is a property of water that is not a health concern, but it can be a nuisance.” So a softener is about scale and soap, not health.
Hardness classes and units
USGS guidelines, in mg/L as calcium carbonate:
| Class | mg/L (ppm) | About gpg |
|---|---|---|
| Soft | 0–60 | 0–3.5 |
| Moderately hard | 61–120 | 3.6–7.0 |
| Hard | 121–180 | 7.1–10.5 |
| Very hard | over 180 | over 10.5 |
To convert, gpg = ppm ÷ 17.1 (and ppm = gpg × 17.1). The calculator does this for you.
If you’re on city water: read your Consumer Confidence Report
Community water systems must give customers an annual water quality report, called a Consumer Confidence Report (CCR). The EPA’s CCR page explains where to find yours; many utilities post it online. Look for “hardness,” “total hardness,” or “calcium” and note the units. Some reports list a range because the utility blends sources, so size for the higher end.
The CCR is also the right place to see what your utility tests for and whether any results exceed EPA limits. A softener doesn’t address those. If something in the report concerns you, ask your utility or local health department what it means for your household.
If you have a private well: test it
No utility tests a private well for you. The EPA’s well-testing guidance (checked 2026-10-19) recommends testing a private well every year for total coliform bacteria, nitrates, total dissolved solids, and pH, and using only state-certified drinking-water labs. It notes your local health department may offer well testing, sometimes for free. The CDC gives the same annual advice.
For softener shopping, the EPA’s own table says to test for hardness when you see scaly residue or soap that won’t lather, and for iron and manganese when a softener is needed. Iron matters for sizing (see How to Size a Water Softener). Ask your health department which other tests make sense where you live.
Test strips and home kits
Hardness test strips and drop kits give a quick estimate and are fine for checking whether a softener is working. For buying decisions, and for anything beyond hardness, a certified lab result is more reliable.
Don’t rely on maps
The USGS publishes national hardness maps but warns they’re “not designed to be used to make local decisions” for an individual home. Use your own report or test.
Next step
Got your number? Plug it into the softener sizing calculator.