What are hardeners?

In connection with the hardness of the water there is talk of hardeners again and again. What these substances are, what properties they have, how they work in the water and whether they are dangerous, this article reveals.

Alkaline earth metals as hardeners

The total hardness of a water is understood to mean the concentration of dissolved alkaline earth metals in the water.

Alkaline earth metals form the second main group of the periodic table. This group includes the substances calcium, magnesium, strontium, barium and beryllium. Radium is also assigned as an intermediate to this group.

As hardeners in the water, all alkaline earth metals except radium and beryllium are responsible. They are dissolved in different ways in the water and make it so hard water.

Alkaline earth metals can be dissolved in the water in different ways. That's why you have to distinguish between temporary water hardness and permanent water hardness.

Properties of the individual substances


Calcium gets into the groundwater mainly through limestone. It is a water-soluble substance that is important for many creatures.

Calcium is needed in the human and animal body for building bones, hair and teeth, trees need calcium for the formation of the leaves, shells for building their shells.


Magnesium is a light metal and also water soluble. In water it forms Mg (OH) 2. Magnesium is flammable and burns quickly forming a bright white flame.

Magnesium is needed in the human and animal body. It is one of the essential nutrients. We also need a comparatively high amount of magnesium daily for the function of our muscles, our nervous system and the metabolism of proteins.


Barium is found in nature only bound, very often as barium sulfate. It has a high reactivity and must therefore always be stored under protective liquids. As barium sulfate, it can not be absorbed by the human body. It therefore often serves as an X-ray contrast agent.


Strontium occurs only in very small amounts in the human body. It probably has no particularly high biological significance and is stored in the bones. Strontium salts may help prevent osteoporosis.

Tips & Tricks

To find out the water hardness in your own residential area, just call the water supplier.

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