Hard water expression method

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Hard water is water that has dissolved mineral (Bi-Carbonate, Sulphate, Chloride of Calcium and Magnesium). Hard water is not health risk. But it creates problem during wet  processing.

Hard water may be classified into two types:

1. Temporary hard water
2. Permanent hard water

Temporary hardness of water can be removed quite easily i.e. by boiling. But permanent hardness can be removed by applying some process. I will discuss these later.

Hardness expression method:

The hardness of water is expressed by the amount of Calcium present in water. In this methods, chloride, sulphates and bi-carbonates of calcium and magnesium are not taken into consideration. Because, it is difficult to measure the components. Hardness is expressed:

PPM (parts per million): PPM is the way to express the dilute concentration of substance. In case of hard water, PPM is the number of grains of calcium carbonate which is present in one million grains of water. It is usually defined as 1mg CaCO₃ per liter and used in America.

In Degree (grains per gallon): The number of grains of Calcium carbonates which are present in 1 gallon (70,000 grains) of water.

Parts per 10⁵: This is the weight of calcium carbonate present in 100000 unit water. It is used in England, France.

So, we find a relationship between PPM and Degree. That is

1000000 grains hard water contains       X        grain CaCO₃

      1               ,,      ,,       ,,            ,,             X / 1000000   ,,       ,,

70,000          ,,       ,,       ,,           ,,        70000 * X/1000000 grains

Hence, Degree of hardness = 0.7 * PPM

PPM = Degree /0.07

Now, let’s take a look about the scale used in different methods to measure the hardness of water.

1⁰dH hardness (German) --> 10mg of CaO  per 1L  water.

1⁰fH hardness (French) --> 10mg of CaCO₃ per 1L water.

1⁰eH hardness (English) --> 1 grain or 68.4mg of CaCO₃ per 4.455L

                                                    water.

                                                    10mg of CaCO₃ per 0.7L water.

1⁰aH hardness (American) --> 1mg of CaCO₃ per 1L water.

gpg hardness --> 1 grain or 68.4mg of CaCO₃ per gallon (US) water.

                                10mg of CaCO₃ per 0.58L water.

If we convert the different system, then we get a table like this:

	Ppm	Gpg	0dH	0eH	0fH
Parts per million (ppm)	1	0.058	0.056	0.07	0.1
Grains per gallon (gpg)	17.118	1	0.96	1.2	1.7
German degree (0dH)	17.80	1.04	1	1.25	1.78
English degree (0eH)	14.30	0.83	0.798	1	1.43
French degree (0fH)	10	0.584	0.56	0.702	1

You can also use a converter to convert the hardness into different method. To convert click here.

Measurement of Hardness of water:

Classification		mg/l or ppm		grains/gal
Soft		0 – 17.1		0 – 1
Slightly hard		17.1 – 60		1 – 3.5
Moderately hard		60 – 120		3.5 – 7.0
Hard		120 – 180		7.0 – 10.5
Very Hard		180 & over		10.5 & over