The ions that cause the hardness of water are calcium and magnesium ions which are abundant in water. In natural waters, calcium and magnesium ions are much more than all other metal ions. For this reason, the hardness of the water is also defined as the calcium carbonate concentration equivalent to the total concentration of all cations present in the water.

The hardness of water is of two types: temporary and permanent. The hardness caused by bicarbonates of metal ions which collapses when heated is called temporary hardness or bicarbonate hardness. The hardness that is caused by sulfate, nitrate and chlorides of metal ions and which does not collapse when heated but can be removed by chemical processes is called permanent hardness. The total of temporary and permanent hardness is defined as total hardness or general hardness.

Water hardness varies from region to region. This situation is related to the geological structure of the region. Generally groundwater is harder than surface water. Hard water is found in areas with limestone and upper soil thick. However, in soft and loose soil areas without limestone, there are softer waters. Hard water is not dangerous for human health. However, hard water generally requires more soap and detergent consumption in cleaning.

Water hardness values ​​range from 10 ppm calcium carbonate to 1800 ppm calcium carbonate. In general, the hardness of the water is as follows:

• 0 = 75 ppm calcium carbonate soft viscosity
• 76 = 150 ppm calcium carbonate medium hardness
• 151 = 300 ppm calcium carbonate hard viscosity
• 300 and above ppm calcium carbonate too hard

Within the scope of chemical analyzes, total hardness determination studies are carried out by spectrophotometric method in authorized laboratories. The spectrophotometric method is based on the measurement of the absorbed or emitted electromagnetic radiation waves of atoms, molecules or ions as they pass from one energy level to another.