Hard water has a high content of dissolved minerals, primarily calcium and magnesium. The hardness level is determined by the amount of these detectable dissolved minerals. In hard water, soap reacts with calcium to form ‘soap scum.’
Hardness can be found in both types of water, tap water and well water. It can range from moderately hard to extremely hard water.
HOW TO MEASURE WATER HARDNESS
In the United States, two commonly used units for measuring water hardness are GPG (Grains per Gallon) and PPM (Parts per Million).
According to the Britannica Encyclopedia, Grain per Gallon (GPG) is a unit of measurement derived from the weight of dry wheat grains. This ancient measurement is equivalent to 1/7000 of a pound.
PPM, which can also be understood as milligrams per liter (mg/L), is exactly as its name suggests: if your water hardness is 1 ppm, then one in a million units of your water is a hardness mineral.
Grain per Gallon (GPG) is a unit of water hardness defined as 1 Grain (64.8 milligrams) of dissolved calcium carbonate in 1 gallon of water (3.79 liters). This is equivalent to 1 part in about 58,000 parts of water, or 17.1 parts per million (ppm).
To compare the relative weight and size of a grain, a standard aspirin tablet typically weighs 5 grains.
Additionally, there are other units of measurement used around the world, such as General Hardness (dGH), German Hardness (°HD), British Hardness (°Clark), and French Hardness (°fH).
CONVERSION OF WATER HARDNESS UNITS
CLASSIFICATION OF WATER ACCORDING TO HARDNESS
