What is Water Hardness

The simple definition of water hardness is the amount of dissolved calcium and magnesium in the water. Hard water is high in dissolved minerals, largely calcium and magnesium. You may have felt the effects of hard water, literally, the last time you washed your hands. Depending on the hardness of your water, after using soap to wash you may have felt like there was a film of residue left on your hands. In hard water, soap reacts with the calcium (which is relatively high in hard water) to form “soap scum”. When using hard water, more soap or detergent is needed to get things clean, be it your hands, hair, or your laundry.

How to Calculate Water Hardness in Grains Per Gallon (GPG)

17.1 mg/L of Hardness (as CaCO₃) = 1 Grain per Gallon

Hardness (mg/L) / 17.1 = GPG Hardness

EXAMPLE

If you have 171 mg/L of Hardness, calculate the hardness in GPG by dividing 171 mg/L by 17.1 like so…

171 mg/L / 17.1 = 10 GPG Hardness