The Water Hardness Scale

More and more homeowners are becoming aware of the problems that having hard water flowing into their homes can cause. Having hard water in your home means that you have to use more detergents and soap to get things clean (including yourself) and it causes scaling on the workings of appliances and boilers that lessen their efficiency and lifespan.

Hard water is caused by minerals that dissolve into it – especially calcium and magnesium. There are “levels” of hard water though and three ways to measure it: grains per gallon, milligrams per liter (mg/L), or parts per million (ppm). The following table is a basic guideline:

Water Hardness Scale
Grains Per Gallon Milligrams Pel Liter (mg/L) or Parts Per Million (ppm) Classification
less than 1.0 less than 17.1 Soft
1.0 – 3.5 17.1 – 60 Slightly Hard
3.5 – 7.0 60 – 120 Moderately Hard
7.0 – 10.5 120 – 180 Hard
over 10.5 over 180 Very Hard

The EPA establishes standards for drinking water but there are no such standards in place for hard water levels, as this can be hard to remedy at the source. When you purchase something like a new dishwasher or washing machine these days there will often be a water hardness recommendation attached to it – you may have to adjust the settings for the level of hardness of your water so therefore it is important to know what that is in your home’s case.

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