Water hardness is measured in grains per gallon (GPG), parts per million (PPM) or milligrammes per litre (MG/L). In the United States, the average water hardness is about 60 GPG, but can range from 0 to over 400 GPG. Water is termed "hard" when it contains large amounts of minerals like calcium and magnesium.
The concentration level gives you an idea of the level of hardness of water:
Anything less than 75 mg/L is considered soft;
76 to 150 mg/L is moderately hard;
151-300 mg/L Hard water;
Very hard water contains more than 300 mg/L.
A general rule of thumb is that water hardness should not surpass 120 to 170 mg/L, or about 7-10 grammes per gallon of water. An accurate water analysis report can help you find out your hardness level whether you get a lab test or do it yourself at your home. You can ask your city's water department for this information, or you can buy one yourself.
