Water is considered soft if total hardness is less than 75 ppm, moderately hard at 75 to 150 ppm, hard at 150 to 300 ppm, and very hard at 300 ppm or higher. To convert the hardness of your water from parts per million to grains per gallon, simply divide by 17.1
Water’s hardness varies with its source. Hard water is not harmful to health, so the choice to buy a water softener is an aesthetic one. However, people on low-sodium diets should be aware that many water softeners increase the sodium content of the water. The hardness of your water is listed in your annual water quality report.