The hardness of drinking water, groundwater or surface water comes from the calcium or magnesium salts contained therein. Hardness is the capacity of water to precipitate soap. Essentially soap is readily precipitated by calcium and magnesium ions, which are always present in water. However, this precipitation is also carried out by precious metals such as iron, aluminum, manganese and zinc and hydrogen ions. Hardness in chemistry is expressed as the amounts of calcium and magnesium ions in terms of calcium carbonate.

Calcium and magnesium bicarbonates show the transient hardness of the water, while chloride, phosphate, nitrate, sulfate and silicates of these elements indicate the permanent hardness of the water.

Since the temporary hardness is derived from bicarbonates, the water is easily removed when boiled. However, since permanent hardness results from calcium and magnesium sulfate and chloride, hardness is not removed even if the water is boiled.

The importance of hard water in the textile sector is that it reduces the life of the fabrics and causes them to wear out.

In order to determine the quality of water, the atomic absorption method used for determination of calcium in water is a sensitive method. In addition, EDTA titrimetric method is widely used in applications. This method is simple and fast.

When EDTA (ethylenediamine tetra acetic acid or its salts) is added to water containing calcium and magnesium, they first combine with calcium. If the pH is high enough, calcium can be determined by EDTA method in a short time. Because if the pH is high, magnesium precipitates as magnesium hydroxide.

In authorized laboratories, Total calcium and magnesium determination analyzes are also performed to determine water quality. The standard used in these studies is as follows:

• TS 4474 ISO 6059 Water quality - Determination of calcium and magnesium total - EDTA titrimetric method

This standard covers the determination of the total concentration of magnesium and calcium in drinking water, groundwater and surface waters by using titrimetric method using ethylenediamine tetra acetic (EDTA).