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Hardness in drinking water

Also called Water hardness, Hard water, Calcium and magnesium, Total hardness (as CaCO3).

Legal limit
None
Health goal
None

Values in parts per million (ppm). Comes from the source.

Where the rules stand

No federal limit. Hardness is not on EPA's primary or secondary standards lists. Values are ppm (mg/L) as calcium carbonate. One grain per gallon equals 17.1 ppm.

What EPA says about health

EPA has no health-based or secondary standard for hardness. WQA's hardness page describes scale buildup in appliances, mineral deposits and stiff laundry, and it does not list health effects.

Where it comes from

Dissolved calcium and magnesium compounds, and sometimes other metals, according to WQA.

What handles it

  • NSF/ANSI 44

    Claim to look for: Hardness Reduction

    NSF listing wording for water softeners. WQA wording: "Hardness."

Sources

  1. National Primary Drinking Water Regulations, U.S. EPA. Checked Oct. 4, 2026.
  2. Secondary Drinking Water Standards: Guidance for Nuisance Chemicals, U.S. EPA. Checked Oct. 4, 2026.
  3. Scale Deposits, Water Quality Association. Checked Oct. 4, 2026.
  4. NSF Standards for Water Treatment Systems, NSF. Checked Oct. 4, 2026.
  5. Search for NSF Certified Drinking Water Treatment Units (standards and reduction claims lists), NSF. Checked Oct. 4, 2026.
  6. Find WQA Certified Products (Gold Seal listings by standard and claim), Water Quality Association. Checked Oct. 4, 2026.