Water hardness scales - how to understand them?

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Water hardness is a term that often appears in the context of water treatment, but not everyone knows how to define it precisely and what the water hardness scales are. In short, water hardness refers to the content of dissolved minerals, primarily calcium (Ca2+) and magnesium (Mg2+) ions, which are derived from salts such as calcium carbonate (CaCO3) and magnesium sulfate (MgSO4). To determine the hardness of water, various hardness scales are used that allow you to express this parameter precisely and understandably.

The basic units of hardness are German degrees (°dH), French degrees (°fH), English degrees (°eH) and milligrams per liter (mg/l). Each of these scales is used in specific regions of the world and has its roots in historical methods of measuring water hardness. Although the values expressed in different units may seem different, it is important that they all refer to the same property of water, and the difference is only due to the different way of expressing it.

Water hardness scales: German (°dH), French (°fH) and English (°eH) degrees

In Germany, Austria and Switzerland, as well as in most of the world, German degrees (°dH) are used to express the hardness of water. On this scale, 1°dH means the content of 10 milligrams of calcium carbonate in 1 liter of water. In other words, if a water sample has a hardness of 10°dH, this means that there are 100 milligrams of calcium carbonate in 1 liter of this water.

The French scale (°fH) is primarily used in France and is slightly different. On this scale, 1°fH means the content of 10 milligrams of calcium carbonate in 1 liter of water, which means that the hardness expressed in French degrees is 1.78 times greater than the same hardness expressed in German degrees.

The English scale (°eH) is used in Great Britain. On this scale, 1°eH corresponds to the content of 14.29 milligrams of calcium carbonate in 1 liter of water. It is therefore the smallest unit among all the scales, which means that the hardness expressed in English degrees will be the largest.

Water hardness scale: milligrams per liter (mg/l)

In some countries, including Poland, the unit milligrams per liter (mg/l) is used to express water hardness. This is the simplest and most intuitive scale because it directly tells us the amount of dissolved minerals in the water. On this scale, 1 mg/l means that there are 1 milligram of dissolved minerals in 1 liter of water. It is therefore a unit that directly relates to the concentration of dissolved minerals, without referring to specific substances such as calcium carbonate.

Understanding the water hardness scales is critical to making the right choice of water treatment system. Water hardness is one of the main parameters we should consider when choosing a system, as different systems are designed to cope with different levels of hardness. By choosing a system that is properly adapted to the hardness of our water, we can enjoy soft and clean water of the highest quality.

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