Tools Hardness Check
Hardness Check Your Water on the USGS Scale
Half of U.S. domestic wells USGS sampled were harder than 162 mg/L. Find where yours sits.
Hardness Check
Enter the number from your water report or test kit, in any unit.
15gpgHard
Against U.S. Domestic Wells
Which Systems Are Rated for It
My Water
Where the Numbers Come From
- Classes: 0–60 mg/L as calcium carbonate is soft, 61–120 moderately hard, 121–180 hard and above 180 very hard (USGS Water Science School).
- Domestic wells: percentiles from about 2,100 private wells sampled 1991–2004 (USGS SIR 2008-5227). That’s a national picture, not your tap.
- Units: 1 gpg = 17.1 mg/L, the factor our calculator uses. 1 °fH = 10 mg/L. 1 °dH = 10 mg/L of calcium oxide, or 17.85 mg/L as calcium carbonate. 1 mmol/L = 100.09 mg/L.
- Your number: on city water it’s in your utility’s annual Consumer Confidence Report. On a private well, test it.
- System limits are the maker’s published maximums from each system page. Systems with no published limit are marked so.
What Changed
New systems, listing changes and tool updates, newest first.