Basically water hardness is measured by the amount of hardness minerals (generally calcium and magnesium) in your water. These amounts are measured in grains per gallon (GPG). The following table illustrates the hardness magnitude of water: Often people say, “I’ve heard of places that are 30 grains hard, or even 60 grains hard. This scale cannot possibly be all encompassing!” The United States has some areas that exceed 100 gpg in hardness, but this scale is based on appliance tolerance to hard water. Take your dishwasher for example: The softer the water, the longer it will last. Under moderately hard water, your dishwasher will last several years–even though it’s not entirely soft water. On the other hand, if you’re on extremely hard water, your dishwasher may only last a few years before hard water completely incapacitates the appliance. Certainly the dishwasher will run on 50 gpg hardness, but its lifespan will be dramatically shortened.