There are some ions in the water. Among these ions, calcium and magnesium ions are the ions that cause water hardening. If these ions are removed from the water, the water is softened. Generally used in homes and tools that soften the tap water, calcium and magnesium ions in the water works in accordance with the principle of removing. Said means include negatively charged ions, which are composed of large water-insoluble molecules and are equilibrated with sodium. As the water to be softened passes through this device, negative ions retain calcium ions instead of sodium. So sodium and calcium ions are replaced. At the end of this process, the amount of calcium in the water decreases and the water softens.

The amount of calcium and magnesium ions in natural waters is much higher than all other metal ions.

The hardness of water is a value that indicates the quality of the water used in homes and industrial plants.

If the source of magnesium and calcium ions dissolved in water is magnesium bicarbonate and calcium bicarbonate, then water can be boiled to precipitate magnesium and calcium as carbonate compounds. After filtration of these precipitates, the remaining water is hardened.

The high degree of hardness of water has no known effect on human health. However, the hardness of the water used in industrial plants may cause the devices used to deteriorate. For this reason, the hardness of the water should be determined and, if necessary, removed. Hard water used causes lime deposits in the devices and disrupts the operation of the vehicles.

The hardness of the water is the temporary hardness of the water rather than the bicarbonate level therein. Because hardness can be removed by boiling water. However, in these cases, the hardness of the water is not due to magnesium and calcium sulfate compounds, but no boiling precipitate and no softening. The hardness of these waters is called permanent hardness. However, the hardness of these waters can also be removed by a number of chemical applications.

Hardness measurements are also performed in accredited laboratories within the scope of water and wastewater measurements.