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Analytical · Glossary

What is Water Hardness?

mg/L as CaCO₃Analytical

Water hardness is the concentration of calcium and magnesium in water, usually expressed as mg/L of calcium carbonate.

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Water Hardness Explained

Hard water forms scale in boilers, heat exchangers and pipes. Softeners and online hardness analysers protect equipment.

Hardness is also stated in German degrees (°dH) or French degrees (°f).

Water Hardness Formula

Hardness = 2.497 × Ca + 4.118 × Mg
Ca, Mgconcentrations in mg/L
Example: Ca 40 mg/L, Mg 12 mg/L: hardness ≈ 149 mg/L as CaCO₃.

Water Hardness: Typical Values

1 °dH17.85 mg/L as CaCO₃
1 °f10 mg/L as CaCO₃
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Calculators for Water Hardness

CalculatorWater Hardness CalculatorFree online calculator with formula and worked example.CalculatorTDS CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is Water Hardness?

Water hardness is the concentration of calcium and magnesium in water, usually expressed as mg/L of calcium carbonate.

What is soft water?

Commonly below about 60 mg/L as CaCO₃; classifications vary.

Does hardness affect conductivity?

Yes, the ions add to conductivity, but conductivity cannot tell hardness from other salts.

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